#### sarahjohnson

##### New member

- Joined
- Jul 20, 2013

- Messages
- 20

8(

*x*

^{2}+

*y*

^{2})

^{2}= 25(

*x*

^{2}−

*y*

^{2})

I got the derivative is

y'(x) = (x (-16 x^2-16 y^2+25))/(y (16 x^2+16 y^2+25))

and then I tried to set top equal to 0 and solve for x^2+y^2 which =25/16

then I plugged this back into the original equation to find x=+or- 15/sqrt(32)

the problem I have is finding y

When I try to plug x back into x^2-y^2 I get a negative root which is undefined?

I get the overall method, just can't get the answer.

Help would be much appreciated. Thanks!

and then I tried to set top equal to 0 and solve for x^2+y^2 which =25/16

then I plugged this back into the original equation to find x=+or- 15/sqrt(32)

the problem I have is finding y

When I try to plug x back into x^2-y^2 I get a negative root which is undefined?

I get the overall method, just can't get the answer.

Help would be much appreciated. Thanks!