Question

Calcule o valor de b e c, onde b/4 = c/2 e b+c = 90.

Answer 1

b/4- c/2=0    *(2)
b+c = 90

b/2- c=0
b+c=90
b/2=90
b=2*90
b=180

Substituindo b em  b+c=90
180+c = 90
c=90-180
c=-90

Answer 2

$\frac{b}{4} = \frac{c}{2} \\ 2b=4c$

Então:
$\left \{ {{2b=4c} \atop {b+c=90}} \right.$

Isolando b:
$b = 90-c$

Aplicando b:
$2(90-c)=4c \\ 180-2c=4c \\ 180=6c \\ \frac{180}{6} = c \\ c=30$

Aplicando c:
$2b = 4(30) \\ 2b = 120 \\ b= \frac{120}{2} \\ b=60$

b = 60
c = 30