Solve the system by the substitution method.
-$xy=56$
$x+y=-15$
A) $\{(7,-8),(8,-7)\}$
B) $\{(-7,8),(-8,7)\}$
C) $\{(-7,-8),(-8,-7)\}$
D) $\{(7,8),(8,7)\}$

Question

Quizplus · Accepted Answer

To solve the system, substitute $y = -15 - x$ into $xy = 56$:  $x(-15 - x) = 56$  $-15x - x^2 = 56$  $x^2 + 15x + 56 = 0$  Factoring gives $(x + 7)(x + 8) = 0$, so $x = -7$ or $x = -8$.  For $x = -7$, $y = -15 - (-7) = -8$.  For $x = -8$, $y = -15 - (-8) = -7$.  Thus, the solutions are $(-7, -8)$ and $(-8, -7)$.

Solve the System by the Substitution Method xy=56xy=56xy=56 x+y=−15x+y=-15x+y=−15 A) {(7,−8),(8,−7)}\{(7,-8),(8,-7)\}{(7,−8),(8,−7)} B) {(−7,8),(−8,7)}\{(-7,8),(-8,7)\}{(−7,8),(−8,7)}

Solve the System by the Substitution Method $xy=56$ $x+y=-15$ A) $\{(7,-8),(8,-7)\}$ B) $\{(-7,8),(-8,7)\}$