Question 110 of 480
Find the area bounded by the curves y = 4 - x2 and y = 2x + 1
- A. 20(1/3) sq. units
- B. 20(2/3) sq. units
- C. 10(2/3) sq. units
- D. 10(1/3) sq. units
Correct Answer:
C
Explanation
To find the area bounded by the curves \( y = 4 - x^2 \) and \( y = 2x + 1 \), we will follow a systematic approach. Here’s a detailed step-by-step explanation of how to solve this problem.
### Step 1: Find the Points of Intersection
First, we need to determine where the two curves intersect. This is done by setting the equations equal to each other:
\[
4 - x^2 = 2x + 1
\]
Rearranging this equation gives:
\[
-x^2 - 2x + 4 - 1 = 0
\]
\[
-x^2 - 2x + 3 = 0
\]
Multiplying through by -1 to make the leading coefficient positive:
\[
x^2 + 2x - 3 = 0
\]
Next, we can factor this quadratic equation:
\[
(x + 3)(x - 1) = 0
\]
Setting each factor to zero gives us the solutions:
\[
x + 3 = 0 \quad \Rightarrow \quad x = -3
\]
\[
x - 1 = 0 \quad \Rightarrow \quad x = 1
\]
Thus, the points of intersection are \( x = -3 \) and \( x = 1 \).
### Step 2: Set Up the Integral for Area
The area \( A \) between the two curves from \( x = -3 \) to \( x = 1 \) can be found using the integral:
\[
A = \int_{-3}^{1} \left( (4 - x^2) - (2x + 1) \right) \, dx
\]
This simplifies to:
\[
A = \int_{-3}^{1} \left( 4 - x^2 - 2x - 1 \right) \, dx
\]
\[
A = \int_{-3}^{1} \left( 3 - x^2 - 2x \right) \, dx
\]
### Step 3: Calculate the Integral
Now we will compute the integral:
\[
A = \int_{-3}^{1} (3 - 2x - x^2) \, dx
\]
We can integrate term by term:
1. The integral of \( 3 \) is \( 3x \).
2. The integral of \( -2x \) is \( -x^2 \).
3. The integral of \( -x^2 \) is \( -\frac{x^3}{3} \).
Thus, we have:
\[
A = \left[ 3x - x^2 - \frac{x^3}{3} \right]_{-3}^{1}
\]
Now we evaluate this expression at the bounds:
1. At \( x = 1 \):
\[
3(1) - (1)^2 - \frac{(1)^3}{3} = 3 - 1 - \frac{1}{3} = 2 - \frac{1}{3} = \frac{6}{3} - \frac{1}{3} = \frac{5}{3}
\]
2. At \( x = -3 \):
\[
3(-3) - (-3)^2 - \frac{(-3)^3}{3} = -9 - 9 + 9 = -9
\]
Now, substituting these values back into the area formula:
\[
A = \left( \frac{5}{3} - (-9) \right) = \frac{5}{3} + 9 = \frac{5}{3} + \frac{27}{3} = \frac{32}{3}
\]
### Step 4: Final Area Calculation
The area \( A \) is:
\[
A = \frac{32}{3} \text{ square units}
\]
### Step 5: Review the Options
Now, let’s compare this result with the provided options:
- A. \( 20(1/3) \) sq. units = \( \frac{20}{3} \)
- B. \( 20(2/3) \) sq. units = \( \frac{40}{3} \)
- C. \( 10(2/3) \) sq. units = \( \frac{20}{3} \)
- D. \( 10(1/3) \) sq. units = \( \frac{10}{3} \)
None of the options match \( \frac{32}{3} \). It appears there may have been a misunderstanding in the options provided or the calculations.
### Summary of Key Points
- **Intersection Points**: Found by setting the equations equal and solving for \( x \).
- **Area Calculation**: Set up the integral of the difference between the two curves.
- **Integral Evaluation**: Carefully compute the definite integral to find the area.
- **Final Result**: The area bounded by the curves is \( \frac{32}{3} \) square units, which does not match the provided options.
### Revision Summary
- Identify points of intersection by solving the equations.
- Set up the area integral as the difference of the two functions.
- Evaluate the integral carefully, ensuring all calculations are correct.
- Double-check the final answer against provided options for accuracy.