Answer :
To convert to polar coordinates, we need to express x and y in terms of r and θ. We have:
x = r cos θ
y = r sin θ
Also, we need to change the limits of integration. The region of integration is the circle centered at the origin with radius 8, so we have:
-π/2 ≤ θ ≤ π/2 (for the upper half of the circle)
0 ≤ r ≤ 8
Now we can express the integrand in terms of r and θ:
[tex]x^2 + y^2 = r^2[/tex] (by Pythagoras)
[tex]20(x^2 + y^2) = 20r^2[/tex]
So the integral becomes:
∫-π/2π/2∫[tex]08r^3 cos^2 θ sin θ dr dθ[/tex]
We can simplify cos^2 θ sin θ using the identity cos^2 θ sin θ = (1/3)sin^3 θ, so we get:
∫-π/2π/2∫[tex]08r^3 (1/3)sin^3 θ dr dθ[/tex]
The integral with respect to r is easy to evaluate:
∫0^8r^3 dr = (1/4)8^4 = 2048
The integral with respect to θ is also easy to evaluate using the fact that sin^3 θ is an odd function:
∫-π/2π/2(1/3)[tex]sin^3[/tex] θ dθ = 0
Therefore, the value of the iterated integral is:
2048(0) = 0
The volume of the solid is zero. This makes sense because the integrand is an odd function of y (or sin θ) and the region of integration is symmetric with respect to the x-axis.
Learn more about polar coordinates
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