Question

calcular el valor de x+2y, luegode rsolver
7x+9y=42
12x+10y= -4

Answer 1

x= (42-9y)/7
x= (-4-10y)/12

(42-9y)/7= (-4-10y)/12
12 (42-9y)= 7(-4-10y)
504-108y = -28-70y
504+28= -70y+108y
532 = 38y
14= y


12x+10y= -4
12x+10(14)= -4
12x= -4-140
12x= -144
x= -12

x+2y
-12+2(14)
-12+28
16

Answer 2

Usaré método de sustitución

7x+9y=42
7x= 42-9y
X= (42-9y)/7

Sustituyo a x en la primera ecuación

12x+10y=-4
12((42-9y)/7)+10y=-4
(504-108y)/7 + 10y=-4
72-108y/7+10 y=-4) X 7
504 -108y + 70 y = -28
(-38y=-532)/-38
Y= 14

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Sustituir el valor de Y en la segunda ecuación

12x+10y= -4
12x+10(14)=-4
12x+140=-4
12x=-144
X=-12
Sustituir en la ecuación dada X+2y -12 + (2 x 14) = -12 + 28= 16