Integration Question! (1 Viewer)

[oh2sxc]

Someone help this is killing me.

The drawing is a bit dodgy but you will get the idea.. Need help!

Cheers.

http://i44.photobucket.com/albums/f43/omrited/MathsQuestion.jpg

 

[insert-username]

Firstly, since we're spinning about the y-axis, you need to rewrite the equation in terms of y:

y = 4 - x²

4 - y = x²

x = ±√(4 - y)

It's a volume, and since we're spinning about the y-axis, we don't need to have the plus/minus (since the volume will go through the plus and minus square roots anyway). So:

pi₀∫⁴[√(4 - y)]² dy

= pi₀∫⁴(4 - y) dy

= pi[4y - y²/2]₀⁴

= pi(16 - 8)

= 8pi units³


I_F

 

[oh2sxc]

shit yeah, cheers mate you saved my afternoon