Calculus: Early Transcendentals, Chapter 6, 6.2, Section 6.2, Problem 39

The formula provided represents the volume of the solid obtained by rotating the region enclosed by the curves y = sqrt(sin x), y = 0, about y axis, using washer method:
V = pi*int_a^b (f^2(x) - g^2(x))dx, f(x)>g(x)
You need to find the endpoints by solving the equation:
sqrt(sin x) = 0 => sin x = 0 => x=0, x = pi
V = pi*int_0^(pi) (sqrt(sin x) - 0)^2)dx
V = pi*int_0^(pi) sin x dx
V = pi*(-cos x)|_0^(pi)
V = pi*(-cos pi + cos 0)
V = pi*(-(-1) + 1)
V = 2pi
Hence, evaluating the volume of the solid obtained by rotating the region enclosed by the curves y = sqrt(sin x), y = 0 , about y axis, using washer method, yields V = 2pi.