Question

se (x-y)² =4 e (x²+y²)=48 quanto é xy

Answer 1

$\sf{(x-y)^2=x^2+y^2-2xy}\\\sf{\implies xy=\dfrac{x^2+y^2-(x-y)^2}{2}}\\\sf{xy=\dfrac{48-4}{2}=\dfrac{42}{2}}\\\huge\boxed{\boxed{\boxed{\boxed{\sf{xy=21}}}}}$