Question

Solve the system by substitution. x = - 4y - 5 2x + 10y = 8

Answer 1

Answer:

x = -41

y = 9

Step-by-step explanation:

Begin by multiplying the top equation by 2

2x = -8y - 10

The second equation requires a little more care.

Start by moving 10y to the right. Normally the y value is on the left, but we are going to be substituting for 2x.

2x = - 10y + 8

What I've done is not the usual practice, but there is nothing wrong with it.

Now since both right sides are equal to 2x, you can substitute for them

-8y - 10 = -10y + 8                Add 10y to both sides

-8y + 10y - 10 = 8

2y - 10 = 8                           Add 10 to both sides

2y = 8+10

2y = 18                                 Divide by 2

y = 18/2

y = 9

Use the second original equation to solve for x

2x + 10y = 8

2x + 10*9 = 8                    

2x + 90 = 8                         Subtract 20 from both sides

2x = 8 - 90

2x =  - 82                              Divide by 2

x = -822/2

x = - 41