Question

$x^{2}$ + $y^{2}$ = 18
xy = 9

Answer 1

$x=frac{9}{y}\ frac{81}{y^2}+y^2=18\ 81+y^4=18y^2\ y^4-18y^2+81=0\ y^2=t\ t^2-18t+81=0\ D=324-4*81=0\ t=frac{18}{2}=9 y=+-3\ x=+-3$