# Calc II finding volume of solid by rotating

MillerGenuine

## Homework Statement

Find the volume of the solid obtained by rotating the region bounded by the given curves about the specified line.

y=x^2
x=y^2

## Homework Equations

Volume= Integral of A(y) dy where A(y)= (pi)(r)^2

## The Attempt at a Solution

My question is how to find the radius portion in the (pi)(r)^2
I know that you subtract the inner radius from the outter radius..and the book says that this is
[(y^1/2) - (-1)]^2 - [y^2 - (-1)]^2

I dont understand how they determined that you subtract (-1) from the function, I realize this is the distance from the roatating axis, by why not [(-1) - (y^1/2)]^2 - ......

how do i determine whether i subtract or add the (1) ?