Question

If x-y=2 and xy=8 then find the value of x^2+y^2

Answer 1

$x-y=2\\(x-y)^2=4\\x^2-2xy+y^2=4\\x^2+y^2=4+2xy\\x^2+y^2=4+2\cdot8\\x^2+y^2=20$