Question

Resolva esse método por substituição
4x-y=0
X+5y=-19

Answer 1

4x-y=0 ⇒ -y=-4x ⇒ y=4x     Substituímos na outra expressão o valor de y:
x+5y=-19 ⇒ x+5*4x=-19 ⇒ x+20x=-19 ⇒ 21x=-19 ⇒ x=-19/21

Agora substituímos o valor exato de x em qualquer uma das expressões e encontramos o valor exato de y:
y=4x ⇒ y=4*-19/21 ⇒ y=-76/21

S= {-19/21; -76/21}

Espero ter ajudado :D :D

Answer 2

$\begin{cases}4x-y=0\\ x+5y=-19\end{cases}\\\\\\ x+5y=-19\to~~ x=-5y-19\\\\\\ 4x-y=0\to~~ 4(-5y-19)-y=0\to~~ -20y-76-y=0\to\\\\ -20-y=76\to~~-21y=76~(-1)\to~~21y=-76\to~~\boxed{y= -\dfrac{76}{21}} \\\\\\ x=-5y-19\to~~ x=-5.\left(-\dfrac{76}{21}\right)-19\to~~ x=\dfrac{380}{21}-19\to\\\\ x=\dfrac{380-399}{21}\to~~ \boxed{x=-\dfrac{19}{21}} \\\\\\\\\\ \large\boxed{\boxed{S=\left\{-\dfrac{19}{21}~;~ -\dfrac{76}{21} \right\}}}$