Question

решите систему уравнений
x/3=-y/4
x+y=5

Answer 1

$left { {{ frac{x}{3}=- frac{y}{4} } atop {x+y=5}} right.$
$left { {{ frac{x}{3}=- frac{y}{4} } atop {x=5-y}} right.$
$left { {{ frac{5-y}{3}=- frac{y}{4} } atop {x=5-y}} right.$
$left { {{ frac{5-y}{3}+frac{y}{4}=0 } atop {x=5-y}} right.$
$left { {{ frac{4(5-y)}{12}+frac{3y}{12}=0 } atop {x=5-y}} right.$
$left { {{ 4(5-y)+3y=0 } atop {x=5-y}} right.$
$left { {{20-4y+3y=0 } atop {x=5-y}} right.$
$left { {{20-y=0 } atop {x=5-y}} right.$
$left { {{y=20 } atop {x=5-y}} right.$
$left { {{y=20 } atop {x=5-20}} right.$
$left { {{y=20 } atop {x=-15}} right.$
ответ: (-15; 20)

Answer 2

$frac{x}{3} =- frac{y}{4}$
$x+y=5      x=5-y$
$frac{5-y}{3} =- frac{y}{4}$
$20-4y=-3y$
$-4y+3y=-20$
$y=20$
$x=5-20$
$x=-15$
ответ($-15;20$)