Question 237 of 480
A polynomial in x whose zeros are -2, -1 and 3 is
- A. x3 - 7x + 6
- B. x3 + 7x - 6
- C. x3 + 7x + 6
- D. x3 - 7x - 6
Correct Answer:
D
Explanation
To determine the correct polynomial whose zeros are -2, -1, and 3, we need to use the fact that if a polynomial has certain zeros, we can express it in factored form. The zeros of a polynomial are the values of \( x \) that make the polynomial equal to zero.
### Step 1: Form the Polynomial from its Zeros
Given the zeros:
- \( x = -2 \)
- \( x = -1 \)
- \( x = 3 \)
We can express the polynomial \( P(x) \) in factored form as follows:
\[
P(x) = (x + 2)(x + 1)(x - 3)
\]
### Step 2: Expand the Polynomial
Now, we will expand this product step by step.
1. **Multiply the first two factors:**
\[
(x + 2)(x + 1) = x^2 + x + 2x + 2 = x^2 + 3x + 2
\]
2. **Now multiply this result by the third factor:**
\[
(x^2 + 3x + 2)(x - 3)
\]
We will distribute \( (x - 3) \) across \( (x^2 + 3x + 2) \):
- First, multiply \( x \) by each term:
\[
x \cdot x^2 = x^3
\]
\[
x \cdot 3x = 3x^2
\]
\[
x \cdot 2 = 2x
\]
- Now, multiply \( -3 \) by each term:
\[
-3 \cdot x^2 = -3x^2
\]
\[
-3 \cdot 3x = -9x
\]
\[
-3 \cdot 2 = -6
\]
3. **Combine all these results:**
\[
P(x) = x^3 + 3x^2 + 2x - 3x^2 - 9x - 6
\]
Combine like terms:
\[
P(x) = x^3 + (3x^2 - 3x^2) + (2x - 9x) - 6
\]
\[
P(x) = x^3 - 7x - 6
\]
### Step 3: Identify the Correct Option
Now that we have derived the polynomial \( P(x) = x^3 - 7x - 6 \), we can compare it with the options provided:
- **A. \( x^3 - 7x + 6 \)**: This is incorrect because the constant term is \( +6 \) instead of \( -6 \).
- **B. \( x^3 + 7x - 6 \)**: This is incorrect because the coefficient of \( x \) is \( +7 \) instead of \( -7 \).
- **C. \( x^3 + 7x + 6 \)**: This is incorrect because both the coefficient of \( x \) and the constant term are incorrect.
- **D. \( x^3 - 7x - 6 \)**: This is correct as it matches our derived polynomial.
### Conclusion
The correct option is **D**: \( x^3 - 7x - 6 \).
### Revision Summary
- A polynomial can be formed from its zeros by using the factored form.
- To find the polynomial, expand the product of the factors corresponding to the zeros.
- Combine like terms carefully to derive the final polynomial.
- Always check each option against the derived polynomial to identify the correct answer.