Question

If $(x + y)^2 = 1$ and $xy = -4$, what is the value of $x^2 + y^2$? Please Help!!

Answer 1

Expanding the first expression gives

$(x+y)^2=x^2+2xy+y^2=1$

Since $xy=-4$, we have

$x^2+2(-4)+y^2=1\implies\boxed{x^2+y^2=9}$