Please explain your answer Identify the integral used to det

Please explain your answer

Identify the integral used to determine the surface area of the surface of revolution for the shape described by y = 1- cos x, -pi/2 x pi/2, revolved about the x-axis.

Solution

ds=sqrt(1+(dy/dx)^2)dx=sqrt(1+sin^2(x))dx

2|y| ds=2|1-cos(x)|sqrt(1+sin^2(x))dx

Answer is 3)