Question

Se x+y=10 e x-y=7, dê o valor numérico de:

 

a)2x+3y

b)-2x+y

c)x/2+y/3

Answer 1

x + y = 10
x - y = 7
x = 10 - y
10 - y - y = 7
-2y = 7 - 10
y = 3/2
x = 10 - 3/2
x = 17/2

a) 2x + 3y
2(17/2) + 3(3/2)
17 + 9/2 = 43/2

b)-2x + y
-17 + 3/2 = -31/2

c) x/2 + y/3
17/2 * 1/2 + 3/2 * 1/3
17/4 + 1/2 = 19/4

Answer 2

 x+y=10
 x-y=7

1º) x+y=10
x= 10-y

2º) x-y=7
10-y -y = 7
-y-y = 7 - 10
-2y = -3 .(-1)
+2y= +3
y= 3/2

Voltando a primeira onde parou para encontrar valor de x.
x= 10-y
x= 10 -3/2   mmc de 1 e 2= 2
x= (20-3)/2
x= 17/2

 x= 17/2   e y= 3/2

a)2x+3y
2.(17/2) + 3.(3/2)
34/2  +  9/2
43/2

b)-2x+y
-2(17/2) + 3/2
-34/2 +3/2
-31/2

c)x/2+y/3
(17/2)/2 + (3/2)/3
17/2 .1/2  + 3/2 . 1/3
17/4 + 3/6           mmc de 4 e 6 = 12
(51 + 6)/12
57/12                  simplificando 57 e 12 por 3
19/4