Hi.

The question asks:

R is the region enclosed by the x-axis, y-axis and the curve.

y = cos^2(x), x&y>= 0

Find the volume by rotating R about the y-axis.

I'm not sure if I'm doing this right.

So the general formula is:

integral A(x) dx

where A(x) is the area of the strip you're using.

So i graphed the function using the cos^2(x) identity and turning it into 1+cos(2x)/2

anyway after rotating the region it only seemed logical to use horizontal strips since they are circles, the A(x) is given by pi r^2 where r is the curve.

Now my question is, since its a horizontal strip we have to integrate wrt to y. do i need to convert y = 1+cos(2x)/2 in terms of x before i integrate?