verify that this is a valid jdf.

f(y1, y2)= 6y1^2 y2 0<=y1<=y2, y1+y2<=2

0 elsewhere

I was trying to integrate y1 from 0 to y2

and y2 from 0 to 2

also i tried y1 from 0 to y2

and y2 from 0 to 1

all times 2

but still not confident with my answers. any help would be great