solve each system by sunbstitution

Question

y=-3x-8

5x+5y=0

Answer 1

y = -3x - 8

5x + 5y = 0

 

5x + 5(-3x - 8) = 0

5x - 15x - 40 = 0

 

Can you solve for x and then y?

Answer 2

The substitution is given since the first equation is y =.

 

Substitute -3x - 8 into the second equation.

 

5x + 5(-3x - 8) = 0. Use distributive rule.

 

5x - 15x - 40 = 0. Combine like terms.

 

-10x - 40 = 0. Add 40 to both sides to isolate x.

 

-10x - 40 + 40 = 0 + 40.

-10x = 40. Divide both sides by -10.

 

-10x/-10 = 40/-10

x = -4.

 

Substitute -4 into fist equation to go directly to y.

 

y = -3(-4) - 8

y = 12 - 8

y = 4

 

Substitute into both equations to check

 

y = -3x - 8             5x + 5y = 0

4 = -3(-4) - 8         5(-4) + 5(4) = 0

4 = 12 - 8              -20 + 20 = 0

4 = 4                     0 = 0

 

Solution is x = -4 and y = 4. (-4,4) written as an ordered pair.