Question

Solve the system by substitution -x - y - z= -8 -4x + 4y + 5z = 7 2x + 2z = 4

Answer 1

First:

2x + 2z = 4

2(x+z)=4

x+z=4/2

x=2-z

-x - y - z=  -8

-(2-z)-y-z= -8         replace x

-2+z-y-z= -8          (cancel z)

-2-y= -8

6 = y

Then:

-4x + 4y + 5z = 7  replace x and y

-4(2-z)+4*6 + 5z = 7

-8 + 4z + 24 + 5z = 7

16 + 9z = 7

9z = 7 - 16

9z = -9

z = -9/9

z= -1

Finally

x= 2-z  replace z

x = 2- (-1)

x = 3