Question 43 of 480
Evaluate ∫1−2(x−1)2dx
- A.
−10
3
−
10
3
- B. 7
- C. 9
- D. 11
Correct Answer:
C
Explanation
To evaluate the integral
\[
\int_{-2}^{1} (x - 1)^{2} \, dx,
\]
we will follow a step-by-step approach.
### Step 1: Expand the Integrand
First, we need to expand the expression \((x - 1)^{2}\):
\[
(x - 1)^{2} = x^{2} - 2x + 1.
\]
### Step 2: Set Up the Integral
Now, we can rewrite the integral with the expanded form:
\[
\int_{-2}^{1} (x^{2} - 2x + 1) \, dx.
\]
### Step 3: Break Down the Integral
We can separate the integral into three simpler integrals:
\[
\int_{-2}^{1} x^{2} \, dx - 2 \int_{-2}^{1} x \, dx + \int_{-2}^{1} 1 \, dx.
\]
### Step 4: Evaluate Each Integral
1. **Evaluate \(\int_{-2}^{1} x^{2} \, dx\)**:
The antiderivative of \(x^{2}\) is \(\frac{x^{3}}{3}\). Thus,
\[
\int_{-2}^{1} x^{2} \, dx = \left[ \frac{x^{3}}{3} \right]_{-2}^{1} = \left( \frac{1^{3}}{3} - \frac{(-2)^{3}}{3} \right) = \left( \frac{1}{3} - \frac{-8}{3} \right) = \frac{1}{3} + \frac{8}{3} = \frac{9}{3} = 3.
\]
2. **Evaluate \(-2 \int_{-2}^{1} x \, dx\)**:
The antiderivative of \(x\) is \(\frac{x^{2}}{2}\). Thus,
\[
-2 \int_{-2}^{1} x \, dx = -2 \left[ \frac{x^{2}}{2} \right]_{-2}^{1} = -2 \left( \frac{1^{2}}{2} - \frac{(-2)^{2}}{2} \right) = -2 \left( \frac{1}{2} - \frac{4}{2} \right) = -2 \left( \frac{1}{2} - 2 \right) = -2 \left( \frac{1 - 4}{2} \right) = -2 \left( \frac{-3}{2} \right) = 3.
\]
3. **Evaluate \(\int_{-2}^{1} 1 \, dx\)**:
The integral of \(1\) over an interval is simply the length of the interval. Thus,
\[
\int_{-2}^{1} 1 \, dx = [x]_{-2}^{1} = 1 - (-2) = 1 + 2 = 3.
\]
### Step 5: Combine the Results
Now, we can combine the results of the three integrals:
\[
3 - 3 + 3 = 3.
\]
### Conclusion
The value of the integral
\[
\int_{-2}^{1} (x - 1)^{2} \, dx = 3.
\]
### Final Answer
The correct option is **A.** \(-\frac{10}{3}\) is incorrect, **B.** \(7\) is incorrect, **C.** \(9\) is incorrect, and **D.** \(11\) is incorrect. The correct answer is **3**.
### Revision Summary
- Expand the integrand before integrating.
- Break down the integral into simpler parts.
- Evaluate each integral separately and combine the results.
- Always check the limits of integration carefully.