Question

Para o caso em que x+y=9 e x- y = 5, quanto vale
$x {}^{2} - y {}^{2}$
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Answer 1

$\Large\boxed{\begin{array}{l}\tt dados\begin{cases}\sf x+y=9\\\sf x-y=5\end{cases}\\\underline{\rm soluc_{\!\!,}\tilde ao\!:}\\\sf x^2-y^2=(x+y)\cdot(x-y)\\\sf x^2-y^2=9\cdot5\\\sf x^2-y^2=45\end{array}}$