# Calculus 2 volume integration, y=axis

Hello, so I've been having lots of trouble with a math problem.
I can differentiate functions but i'm kinda confused on what to do when it is like y=4

So say you have the given: y= x^2 and then y=4, x=0, x=2. Rotate about the y-axis.
I'm know you have to get it into respect to y so x=sqrt(y) but what would I do from there?! you can't put x in terms of y for y=4! i'm confused. Can somebody help me out or point me in the right direction.

mathwonk
Homework Helper
they are giving you 4 different curves or lines and you are supposed to envision the region bounded by those curves or lines. so you have the line y=4 at the top, y=x^2 on the right, .......

ooops, your equations do not fit together to give one region. you need to re - read the question.

Okay well the y=x^2 is a parabola so it goes on both sides of the y-axis. And then the y=4 is another bounding line.

we are supposed to rotate the bounded region from x=0 to 2 around the y-axis.

I'm just confused on how to rotate it around like that.

mathwonk