Algebra question - quick visual

[vorcil]

It's a physics question but I need help solving for the radius in the picture bellow
I need to solve for r so i can finish my physics question off
http://www.freeimagehosting.net/uploads/th.dc286819a1.jpgmy work so far

(r-y)^2 + L^2 = r^2

r^2 - (2*r*y) + y^2 + L^2 = r^2

I'm not to sure how to solve this from here
algebraically, for r

 

[lanedance]

subtract r^2 from both sides, then divide everything by -2y

 

[vorcil]

subtract r^2 from both sides, then divide everything by -2y

bah I didn't see how friggen simple it was
I thought I had to pull out some hardcore mathematics

If I had continued and just removed r^2 in the first place instead of asking what to do

-2ry+y^2+l^2
2ry = y^2 + L^2
r = (y^2)+(L^2) / 2y

cheers big ears

 

[flatmaster]

Carefull now. Remember that the 2y is dividing the entire right-hand side, not just the L^2