Question

Qual dos pares a seguir faz parte do conjunto de soluções do sistema
{×-y=25
{2× + 3y -40

A(30,5).
B.(34,9)
C.(5-20)
d.(7.-18)​

Answer 1

$\left\{ \begin{array}{c} x - y = 25 \\ 2x+3y=-40 \end{array}\right.\\\\\left\{ \begin{array}{c} x - y = 25 \mbox{ } (-2) \\ 2x+3y=-40 \end{array}\right.\\\\\left\{ \begin{array}{c} -2x + 2y = -50 \\ 2x+3y=-40 \end{array}\right.\\\\\\5y = -50-40\\5y=-90\\\displaystyle y = \frac{-90}{5} = -18\\\\x-y=25\\x-(-18)=25\\x+18=25\\x=25-18\\x=7$

Alternativa D.