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gloria22488's Question
Math
Posted 10 months ago
22(x3cosx2+12)4x2dx\int_{-2}^{2}\left(x^{3} \cos \frac{x}{2}+\frac{1}{2}\right) \sqrt{4-x^{2} d x}
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Answer from Sia
Posted 10 months ago
Solution by Steps
step 1
Evaluate the definite integral of the given function over the interval from -2 to 2
step 2
The function to integrate is 4x2(12+x3cos(x2))\sqrt{4 - x^2} \left(\frac{1}{2} + x^3 \cos\left(\frac{x}{2}\right)\right)
step 3
The integral is symmetric around the y-axis, and the function x3cos(x2)x^3 \cos\left(\frac{x}{2}\right) is an odd function, which will integrate to zero over the symmetric interval
step 4
The remaining function to integrate is 124x2\frac{1}{2} \sqrt{4 - x^2}, which is an even function
step 5
The integral of an even function over a symmetric interval can be computed as twice the integral from 0 to the upper limit
step 6
Compute the integral 02124x2dx\int_{0}^{2} \frac{1}{2} \sqrt{4 - x^2} dx
step 7
Recognize that 4x2\sqrt{4 - x^2} represents a semicircle with radius 2, and the integral computes the area of a semicircle
step 8
The area of a semicircle with radius 2 is 12πr2=12π(2)2=2π\frac{1}{2} \pi r^2 = \frac{1}{2} \pi (2)^2 = 2\pi
step 9
Multiply the area by 12\frac{1}{2} to account for the coefficient in the integral
step 10
The final result is 122π=π\frac{1}{2} \cdot 2\pi = \pi
Answer
π\pi
Key Concept
Symmetry in Integration
Explanation
The integral of an odd function over a symmetric interval is zero, and the integral of an even function can be simplified by considering only half of the interval and doubling the result. In this case, the odd part of the function integrates to zero, and the even part corresponds to the area of a semicircle.

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