The question is:

Please click the picture above.

I let x^2+y^2=a^2 be the vertical cylinder, and I tried to find

1)the intersections between x^2+y^2=a^2 and z=2xy

2)the intersections between x^2+y^2=a^2 and z=x^2+y^2

and then don't know how to do.

I need to show the two area is the same, but i don't know how to show.