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

Answer 1

let ab = x
let cd = y

2 x + 5 y = 5
x y = 1 so y = 1/x

etc

in the end you want
4 x^2
and
25 y^2