solve each system by substitution

Question

solve each system by substitution

question 1.

x + 8y = -15

7x +8y =-9

question 2

-5x - 7y =11

x - 2y= -9

Answer 1

Question 1:

x + 8y = -15

7x + 8y = -9

Solve by substitution:

8y = -15 - x

8y = -9 - 7x

Substitute 8y with each other

-15 - x = -9 - 7x

-x + 7x = -9 + 15

6x = 6

x = 1

x + 8y = -15

1 + 8y = -15

8y = -16

y = -2

x = 1 , y = -2

Question 2:

-5x - 7y = 11

x - 2y= -9 => x = -9 + 2y

Substitute that x equation into the first one

-5( -9 + 2y ) - 7y = 11

45 - 10y - 7y = 11

-17y = 11 - 45

-17y = -34

y = 2

Substitute y = 2 into any equation

x - 2y= -9

x - 2(2) = -9

x -4 = -9

x = -9 + 4

x = -5

x=-5, y=2