Question

resolva os sistema utilizando o metodo da substituiçao
a) (x + y=10
x - y=2
b)(x - y=14
x - y =4
c)(x + y =21
x- y =1
d)(x + y =12
x - y =2
e)(x + 1 =y
x + y =15
f)( x - 6=y
x + y= 18

Answer 1

a)
x + y = 10
x - y = 2

Isolar "x" em II:
x = 2 + y

x + y = 10
2 + y + y = 10
2y + 2 = 10
2y = 10 - 2
2y = 8
y = 8/2
y = 4

x + y = 10
x + 4 = 10
x = 10 - 4
x = 6
------------------------------------------------------------
b)
x - y = 14
x - y  = 4

x - y = 4
x = 4 + y

x - y = 14
4 + y - y = 14
4 + 0 = 14 
(sistema impossível)
---------------------------------------------------------
c)
x + y =21
x - y = 1

x - y = 1
x = 1 + y

x + y = 21
1 + y + y = 21
2y = 21 - 1
2y = 20
y = 20/2
y = 10

x = 1 + y
x = 1 + 10
x = 11

d)
x + y =12
x - y =2

x - y = 2
x = 2 + y

x + y = 12
2 + y + y = 12
2y = 12 - 2
2y = 10
y = 10/2
y = 5

x = 2 + y
x = 2 + 5
x = 7

============================
e)
x + 1 = y
x + y =15 

y = x + 1

x + y = 15
x + x + 1 = 15
2x = 15 - 1
2x = 14
 x = 14/2
x = 7

x + 1 = y
7 + 1 = y
8 = y
y = 8
------------------------------------------------------------
f)
x - 6 = y
x + y = 18

y = x - 6

x + y = 18
x + x - 6 = 18
2x = 18 + 6
2x = 24
x = 24/2
x = 12

y = x - 6
y = 12 - 6
y = 6