Question

3) x² + y² = 58, x² - y² = 40;​

Answer 1

$\begin{cases}x^2+y^2=58\\ x^2-y^2=40\end{cases}\Rightarrow 2x^2=98\Leftrightarrow x^2=49\Rightarrow x=\pm 7\\x=\pm7\Rightarrow y^2=58-49=9\Rightarrow y=\pm 3$