Question

If 2ab + 5cd = 5 and abcd = 1, what is the value of 4a^2b^2+ 25 c^2d^2

Answer 1

You have u^2+v^2, where
u = 2ab
v = 5cd

As you know, (u+v)^2 = u^2+2uv+v^2

Now just plugin your substitutions.