Question

a) x+y=1
x-y=8





b) x-y=18
x+y=8




c) x+y=24
x-y=8

Answer 1

a) x + y = 1            
    x - y = 8 
   2x = 9
    x = 9/2

y = 1 - x
y = 1 - 9 ==> y = 2-9  ==> y = - 7
           2                2                  2
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b) x-y=18
     x+y=8
     2x = 26 ==> x = 13

x+y=8 ==> y = 8 - x ==> y = 8 - 13 ==> y = - 5
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c) x+y=24
     x-y=8
    2x = 32
     x = 16

 x+y=24 ==> y = 24 - x ==> y = 24-16 ==> y = 8

Answer 2

A) x-y=8
    x=8+y

x+y = 1
(8+y)+y = 1
 8+2y = 1
     2y = 1-8
       y=-7/2
x+y=1
x-7/2 = 1
x=1+7/2
x=9/2

B)
  Podemos somar as duas equações
    x-y=18
    x+y= 8
   2x   = 26
     x   = 13
x-y  = 18
13 - y = 18
13-18 = y
   
      y = -6



C)x+y= 24
    x -y = 8
    2x = 32
     x  = 16

x-y = 8
16-y = 8
16-8 = y
 y = 8