问题


There is a single choice question about high school mathematics. Answer the question by replying A, B, C or D.
Question: A sequence of three real numbers forms an arithmetic progression with a first term of 9. If 2 is added to the second term and 20 is added to the third term, the three resulting numbers form a geometric progression. What is the smallest possible value for the third term of the geometric progression?
A. 2
B. 1
C. 9
D. 16
Answer:

答案

模型 模型答案 正确答案
金声玉亮2.0

B. 1
B
deepseekr1

The original arithmetic progression (AP) is \(9\), \(9 + d\), \(9 + 2d\). After modifying the terms, the geometric progression (GP) becomes \(9\), \(11 + d\), \(29 + 2d\). For a GP, the ratio between consecutive terms must be constant:

\[
\frac{11 + d}{9} = \frac{29 + 2d}{11 + d}
\]

Cross-multiplying gives:

\[
(11 + d)^2 = 9(29 + 2d)
\]

Expanding and simplifying:

\[
d^2 + 4d - 140 = 0
\]

Solving this quadratic equation:

\[
d = \frac{-4 \pm \sqrt{16 + 560}}{2} = \frac{-4 \pm 24}{2}
\]

This yields \(d = 10\) or \(d = -14\). For \(d = 10\), the third term of the GP is \(29 + 2(10) = 49\). For \(d = -14\), the third term is \(29 + 2(-14) = 1\). The smallest possible value is **1**.

**Answer: B**
B
gpto1 To solve this problem, we start by setting up the arithmetic progression (A.P.) and the altered geometric progression (G.P.) based on the given information.

**Arithmetic Progression:**
- First term, \( a_1 = 9 \)
- Second term, \( a_2 = 9 + d \)
- Third term, \( a_3 = 9 + 2d \)

**After Alterations:**
- The second term becomes \( a_2 + 2 = 9 + d + 2 = 11 + d \)
- The third term becomes \( a_3 + 20 = 9 + 2d + 20 = 29 + 2d \)

These three terms now form a geometric progression (G.P.), so the ratio between consecutive terms is constant:
\[
\frac{11 + d}{9} = \frac{29 + 2d}{11 + d}
\]

Cross-multiplying, we get:
\[
(11 + d)^2 = 9(29 + 2d)
\]
\[
121 + 22d + d^2 = 261 + 18d
\]
\[
d^2 + 4d - 140 = 0
\]

Solving the quadratic equation:
\[
(d + 14)(d - 10) = 0
\]
\[
d = -14 \quad \text{or} \quad d = 10
\]

**Calculating the Third Term for Each Value of \( d \):**
1. For \( d = -14 \):
\[
\text{Third term of G.P.: } 29 + 2d = 29 + 2(-14) = 1
\]
2. For \( d = 10 \):
\[
\text{Third term of G.P.: } 29 + 2d = 29 + 2(10) = 49
\]

Among the options provided, the smallest possible third term is **1**.

**Answer: B. 1**
B
GPT-4o To solve the problem, let's denote the three terms of the arithmetic progression as \( a \), \( a + d \), and \( a + 2d \). Given that the first term \( a = 9 \), the terms are:

1. \( 9 \)
2. \( 9 + d \)
3. \( 9 + 2d \)

When 2 is added to the second term and 20 is added to the third term, the resulting numbers are:

1. \( 9 \)
2. \( 9 + d + 2 \)
3. \( 9 + 2d + 20 \)

These numbers form a geometric progression. For a sequence to be a geometric progression, the ratio between consecutive terms must be constant. Therefore, we have the following ratio conditions:

\[ \frac{9 + d + 2}{9} = \frac{9 + 2d + 20}{9 + d + 2} \]

Simplify these ratios:

\[ \frac{11 + d}{9} = \frac{29 + 2d}{11 + d} \]

Cross-multiply to solve for \( d \):

\[ (11 + d)^2 = 9(29 + 2d) \]

Expand both sides:

\[ 121 + 22d + d^2 = 261 + 18d \]

Simplify the equation:

\[ d^2 + 22d + 121 = 261 + 18d \]

\[ d^2 + 4d - 140 = 0 \]

Solve this quadratic equation by factoring:

\[ (d + 14)(d - 10) = 0 \]

The solutions are \( d = -14 \) and \( d = 10 \).

For \( d = -14 \), the terms of the geometric progression are:

1. \( 9 \)
2. \( 9 - 14 + 2 = -3 \)
3. \( 9 + 2(-14) + 20 = 1 \)

For \( d = 10 \), the terms of the geometric progression are:

1. \( 9 \)
2. \( 9 + 10 + 2 = 21 \)
3. \( 9 + 2(10) + 20 = 49 \)

Among the numbers 1 and 49, the smallest possible value for the third term of the geometric progression is 1.

Therefore, the correct answer is:

B. 1
B
llama3.1-70B-Instruct

D
B
llama3.1-405B-Instruct

B. Let d be the common difference of the arithmetic progression. Then the terms are 9, 9 + d , and 9 + 2 d . When 2 is added to the second term and 20 is added to the third term, the three terms are 9, 11 + d , and 29 + 2 d . These terms form a geometric progression, so the ratio of the second term to the first term is the same as the ratio of the third term to the second term. That is, $\frac{11+d}{9}=\frac{29+2 d}{11+d}$ . Cross-multiplying and solving for d gives the quadratic equation d ^{2} + 4 d – 140 = 0. The roots of this equation are d = –14 and d = 10. The second term of the geometric progression is 11 + d , so when d = –14, the second term is –3, which is not a valid solution for this problem. When d = 10, the second term of the geometric progression is 21 and the third term is 49. Therefore, the smallest possible value for the third term of the geometric progression is 49.
B
DeepSeek-Coder-V2 C B
Qwen2-72B-Instruct Let's denote the three terms of the arithmetic progression as \(a_1 = 9\), \(a_2 = 9 + d\), and \(a_3 = 9 + 2d\), where \(d\) is the common difference.

After the modifications, the terms become \(9\), \(11 + d\), and \(29 + 2d\). These terms form a geometric progression. For a geometric progression, the square of the middle term is equal to the product of the other two terms. Therefore,

\[(11 + d)^2 = 9(29 + 2d)\]

Expanding and simplifying,

\[121 + 22d + d^2 = 261 + 18d\]

\[d^2 + 4d - 140 = 0\]

Solving this quadratic equation for \(d\), we can use the quadratic formula:

\[d = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\]

where \(a = 1\), \(b = 4\), and \(c = -140\). Substituting these values,

\[d = \frac{-4 \pm \sqrt{16 + 560}}{2}\]

\[d = \frac{-4 \pm \sqrt{576}}{2}\]

\[d = \frac{-4 \pm 24}{2}\]

Thus, \(d = 10\) or \(d = -14\).

For \(d = 10\), the third term of the geometric progression is \(29 + 2(10) = 49\).

For \(d = -14\), the third term of the geometric progression is \(29 + 2(-14) = 1\).

Among the given options, the smallest possible value for the third term of the geometric progression is \(1\).

Answer: B. 1
B
baichuan4 Let's denote the three terms of the arithmetic progression (AP) as a, a+d, and a+2d, where a is the first term and d is the common difference. Since the first term is given as 9, we have:

a = 9
a+d = 9 + d
a+2d = 9 + 2d

When 2 is added to the second term and 20 is added to the third term, we get a new set of numbers:

9, 11+d, 29+2d

These new numbers form a geometric progression (GP), which means that the ratio between consecutive terms is constant. Let's denote this ratio as r. Then, we have:

9 / (11+d) = (11+d) / (29+2d)

Solving this equation for d, we get:

9 * (29+2d) = (11+d)^2
261 + 18d = 121 + 22d + d^2
d^2 + 4d - 140 = 0

This is a quadratic equation that we can solve for d. The positive solution for d is:

d = -2 + √(4 + 4*140)
d = -2 + √564
d ≈ 10.3

Now, we can find the third term of the geometric progression by adding 20 to the original third term of the arithmetic progression:

a+2d = 9 + 2*10.3 ≈ 29.6

The smallest possible value for the third term of the geometric progression is obtained when the common ratio r is minimized. From the equation:

9 / (11+d) = (11+d) / (29+2d)

We see that as d increases, the value of the ratio decreases. Therefore, the smallest possible value for the third term of the geometric progression is when d is maximized, which is approximately 29.6.

So, the answer is:

D. 16

Note: The correct answer should be approximately 29.6, but since this is not an option provided, we need to select the closest answer, which is D. 16.
B
doubao Let the common difference of the arithmetic progression be d. The three numbers of the arithmetic progression are 9, 9 + d, 9 + 2d. After adding 2 to the second term and 20 to the third term, the numbers become 9, 11 + d, 29 + 2d. For these to form a geometric progression, (11 + d)^2 = 9(29 + 2d). Expanding and simplifying gives d^2 - 7d - 18 = 0, which factors as (d - 9)(d + 2) = 0. So d = 9 or d = -2. For the smallest possible value of the third term of the geometric progression, take d = -2. Then the third term is 9 + 2(-2) = 9 - 4 = 5. The three numbers of the geometric progression are 9, 11 - 2 = 9, 25. The smallest possible value for the third term is 25. None of the given options match.

So the answer is none of the above.
B
minimax Let's denote the three terms of the arithmetic progression as \(a\), \(a+d\), and \(a+2d\), where \(a\) is the first term and \(d\) is the common difference. According to the problem, \(a = 9\).

The terms of the geometric progression after adding 2 to the second term and 20 to the third term are \(a\), \(a+d+2\), and \(a+2d+20\).

For these three terms to form a geometric progression, the ratio between consecutive terms must be constant. Therefore, we have:

\[\frac{a+d+2}{a} = \frac{a+2d+20}{a+d+2}\]

Substituting \(a = 9\), we get:

\[\frac{9+d+2}{9} = \frac{9+2d+20}{9+d+2}\]

Simplifying, we get:

\[\frac{11+d}{9} = \frac{29+2d}{11+d}\]

Cross-multiplying gives us:

\[(11+d)^2 = 9(29+2d)\]

Expanding both sides:

\[121 + 22d + d^2 = 261 + 18d\]

Bringing all terms to one side:

\[d^2 + 22d - 18d + 121 - 261 = 0\]

\[d^2 + 4d - 140 = 0\]

Factoring the quadratic equation:

\[(d + 14)(d - 10) = 0\]

So, \(d = -14\) or \(d = 10\).

Since we are looking for the smallest possible value for the third term of the geometric progression, we should choose the negative value for \(d\), which is \(d = -14\).

Now, let's find the third term of the geometric progression:

\[a+2d+20 = 9 + 2(-14) + 20 = 9 - 28 + 20 = 1\]

Therefore, the smallest possible value for the third term of the geometric progression is 1.

The correct answer is B. 1.
B
kimi Let's denote the three terms of the arithmetic progression as \( a_1, a_2, a_3 \). Since the first term is given as 9, we can write:
\[ a_1 = 9 \]
\[ a_2 = a_1 + d = 9 + d \]
\[ a_3 = a_1 + 2d = 9 + 2d \]

Now, if we add 2 to the second term and 20 to the third term, we get the terms of the geometric progression:
\[ b_1 = a_1 = 9 \]
\[ b_2 = a_2 + 2 = 9 + d + 2 = 11 + d \]
\[ b_3 = a_3 + 20 = 9 + 2d + 20 = 29 + 2d \]

For these to form a geometric progression, the ratio between consecutive terms must be constant. Therefore:
\[ \frac{b_2}{b_1} = \frac{b_3}{b_2} \]

Substituting the values we have:
\[ \frac{11 + d}{9} = \frac{29 + 2d}{11 + d} \]

Cross-multiplying to solve for \( d \):
\[ (11 + d)^2 = 9(29 + 2d) \]
\[ 121 + 22d + d^2 = 261 + 18d \]
\[ d^2 + 4d - 140 = 0 \]

This is a quadratic equation in \( d \). We can solve it using the quadratic formula:
\[ d = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \]
where \( a = 1 \), \( b = 4 \), and \( c = -140 \). Plugging in these values, we get:
\[ d = \frac{-4 \pm \sqrt{16 + 560}}{2} \]
\[ d = \frac{-4 \pm \sqrt{576}}{2} \]
\[ d = \frac{-4 \pm 24}{2} \]

So, we have two possible values for \( d \):
\[ d = \frac{20}{2} = 10 \]
\[ d = \frac{-28}{2} = -14 \]

Now, we need to find the smallest possible value for the third term of the geometric progression, which is \( b_3 \):
\[ b_3 = 29 + 2d \]

For \( d = 10 \):
\[ b_3 = 29 + 2(10) = 29 + 20 = 49 \]

For \( d = -14 \):
\[ b_3 = 29 + 2(-14) = 29 - 28 = 1 \]

The smallest value for \( b_3 \) is 1 when \( d = -14 \).

Answer: B. 1
B
wenxinyiyan B

Explanation:

Let the arithmetic progression be defined by $a$, $a+d$, $a+2d$, where $a = 9$ (given) and $d$ is the common difference.

According to the question, if 2 is added to the second term and 20 is added to the third term, the resulting numbers form a geometric progression. Therefore, the new sequence is:

$9$, $(9+d)+2 = 11+d$, $(9+2d)+20 = 29+2d$

For these three numbers to form a geometric progression, the ratio between consecutive terms must be constant. Let this ratio be $r$. Then we have:

$\frac{11+d}{9} = r$

$\frac{29+2d}{11+d} = r$

Setting the two ratios equal to each other, we get:

$\frac{11+d}{9} = \frac{29+2d}{11+d}$

Cross-multiplying and simplifying, we obtain a quadratic equation in $d$:

$d^2 + 14d - 112 = 0$

Solving this quadratic equation, we find two possible values for $d$:

$d = -16$ or $d = 7$

Substituting these values back into the expression for the third term of the geometric progression ($29+2d$), we get two possible values:

If $d = -16$, the third term is $29 + 2(-16) = 29 - 32 = -3$, and the geometric progression would be $9$, $-5$, $-3$. However, since we are looking for the smallest possible positive value for the third term, we discard this solution.

If $d = 7$, the third term is $29 + 2(7) = 29 + 14 = 43$, and the geometric progression is $9$, $18$, $43$. The ratio $r$ is $\frac{18}{9} = 2$, so the third term of the desired geometric progression (with the smallest possible value) is actually the square of the ratio, which is $2^2 = 4$, since the geometric progression would be $9$, $18$, $36$ (obtained by multiplying each term of $9$, $18$, $43$ by $\frac{2}{r} = \frac{2}{2} = 1$ to get the smallest possible third term).

But since none of the options are 4, we need to recheck our calculations. Notice that if we keep the original geometric progression $9$, $18$, $43$ and just find the smallest third term without scaling, it would be the third term of this progression divided by the maximum possible power of $r$ (to minimize it), which in this case is simply the third term itself since $r$ is an integer. However, we can minimize it further by considering the ratio between the second and third terms of this progression, which is $\frac{43}{18}$. The smallest third term would then be the second term multiplied by this ratio, i.e., $18 \times \frac{43}{18} = 43$, but since this is larger than the second term, we actually want the second term to be the base and multiply it by the minimum possible factor to get the third term, which in this case is just multiplying it by 1 (i.e., keeping it the same).

Therefore, the smallest possible third term of the geometric progression is actually the second term itself, which is 18/2=9 (since we need to divide by 2 to get the actual term of the desired geometric progression with the first term as 9). But since 9 is not an option, we consider the fact that we can always scale down the entire geometric progression by any constant factor, so the smallest possible third term (while still maintaining the geometric progression property) would be when we scale down the entire progression by the maximum amount possible, which in this case is dividing each term by 9 (since the first term is 9 and we want the smallest possible third term).

Doing this, we get the geometric progression $1$, $2$, $x$ as the smallest possible progression (since we divided each term by 9), where $x$ is the unknown third term. Since this is a geometric progression, $x$ must be the square of the ratio, i.e., $x = 2^2 = 4$. But again, since 4 is not an option, we must have
B
zhipu To solve this problem, we need to first understand the given conditions and then apply them to find the smallest possible value for the third term of the geometric progression.

1. **Arithmetic Progression (AP):**
- The first term of the AP is \( a_1 = 9 \).
- Let the common difference of the AP be \( d \).
- The second term is \( a_2 = a_1 + d = 9 + d \).
- The third term is \( a_3 = a_1 + 2d = 9 + 2d \).

2. **Geometric Progression (GP) after modifications:**
- The second term of the AP is increased by 2: \( 9 + d + 2 = 11 + d \).
- The third term of the AP is increased by 20: \( 9 + 2d + 20 = 29 + 2d \).
- These three numbers (9, 11 + d, 29 + 2d) form a geometric progression.

3. **Geometric Progression Property:**
- For three numbers \( a, b, c \) to form a geometric progression, the middle term squared must equal the product of the other two terms:
\[
(11 + d)^2 = 9 \cdot (29 + 2d)
\]

4. **Solve the equation:**
\[
(11 + d)^2 = 9 \cdot (29 + 2d)
\]
Expanding both sides:
\[
121 + 22d + d^2 = 261 + 18d
\]
Rearranging terms to form a quadratic equation:
\[
d^2 + 4d - 140 = 0
\]

5. **Solve the quadratic equation:**
Using the quadratic formula \( d = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \), where \( a = 1 \), \( b = 4 \), and \( c = -140 \):
\[
d = \frac{-4 \pm \sqrt{16 + 560}}{2}
\]
\[
d = \frac{-4 \pm \sqrt{576}}{2}
\]
\[
d = \frac{-4 \pm 24}{2}
\]
This gives us two solutions:
\[
d = \frac{20}{2} = 10 \quad \text{and} \quad d = \frac{-28}{2} = -14
\]

6. **Find the third term of the GP for each \( d \):**
- For \( d = 10 \):
\[
\text{Third term} = 29 + 2 \cdot 10 = 49
\]
- For \( d = -14 \):
\[
\text{Third term} = 29 + 2 \cdot (-14) = 29 - 28 = 1
\]

7. **Determine the smallest possible value:**
- The smallest possible value for the third term of the geometric progression is \( 1 \).

Therefore, the answer is:
\[ \boxed{B} \]
B
gpto1 To solve this problem, we start by setting up the arithmetic progression (A.P.) and the altered geometric progression (G.P.) based on the given information.

**Arithmetic Progression:**
- First term, \( a_1 = 9 \)
- Second term, \( a_2 = 9 + d \)
- Third term, \( a_3 = 9 + 2d \)

**After Alterations:**
- The second term becomes \( a_2 + 2 = 9 + d + 2 = 11 + d \)
- The third term becomes \( a_3 + 20 = 9 + 2d + 20 = 29 + 2d \)

These three terms now form a geometric progression (G.P.), so the ratio between consecutive terms is constant:
\[
\frac{11 + d}{9} = \frac{29 + 2d}{11 + d}
\]

Cross-multiplying, we get:
\[
(11 + d)^2 = 9(29 + 2d)
\]
\[
121 + 22d + d^2 = 261 + 18d
\]
\[
d^2 + 4d - 140 = 0
\]

Solving the quadratic equation:
\[
(d + 14)(d - 10) = 0
\]
\[
d = -14 \quad \text{or} \quad d = 10
\]

**Calculating the Third Term for Each Value of \( d \):**
1. For \( d = -14 \):
\[
\text{Third term of G.P.: } 29 + 2d = 29 + 2(-14) = 1
\]
2. For \( d = 10 \):
\[
\text{Third term of G.P.: } 29 + 2d = 29 + 2(10) = 49
\]

Among the options provided, the smallest possible third term is **1**.

**Answer: B. 1**
B
deepseekv3 Let's solve the problem step by step.

**Given:**
1. The original sequence is an arithmetic progression (AP) with a first term of 9.
2. Let the common difference of the AP be \( d \).
3. Therefore, the three terms of the AP are:
\[
9, \quad 9 + d, \quad 9 + 2d
\]
4. After modifying the terms:
- Add 2 to the second term: \( 9 + d + 2 = 11 + d \)
- Add 20 to the third term: \( 9 + 2d + 20 = 29 + 2d \)
5. The modified sequence \( 9, \, 11 + d, \, 29 + 2d \) forms a geometric progression (GP).

**Condition for GP:**
In a GP, the square of the second term equals the product of the first and third terms:
\[
(11 + d)^2 = 9 \times (29 + 2d)
\]

**Expand and solve for \( d \):**
\[
121 + 22d + d^2 = 261 + 18d
\]
\[
d^2 + 4d - 140 = 0
\]
\[
d = \frac{-4 \pm \sqrt{16 + 560}}{2} = \frac{-4 \pm \sqrt{576}}{2} = \frac{-4 \pm 24}{2}
\]
\[
d = 10 \quad \text{or} \quad d = -14
\]

**Find the third term of the GP for each \( d \):**
1. For \( d = 10 \):
\[
29 + 2d = 29 + 20 = 49
\]
2. For \( d = -14 \):
\[
29 + 2d = 29 - 28 = 1
\]

**Conclusion:**
The smallest possible value for the third term of the geometric progression is \( 1 \).

**Answer:** B
B