Solve the system of linear equations by substitution. Check your solution.

Question

y= x - 4

-2x + y = 18

Answer 1

As of now, you know:

y= x - 4

Substitute x - 4 for y in your other equation to have the same variable in one equation, to be able to solve for x.

-2x + x - 4 = 18

You then begin to solve by trying to isolate the variable. Remember, whatever you do to one side, you do to the other. The equation is subtracting 4, therefore you will want to add 4 to both sides.

-2x + x = 22

Then you can combine your like terms, -2x and x.

-x = 22

x cannot be negative. The coefficient before a single variable is always 1, so -x is the same as -1x. You will need to divide each side by -1 so we are left with a single x on the left.

x = -22

Now that you know what x equals, you can substitute that value in your other equation to solve for y.

y = -22 - 4

I like to change subtraction to addition, to eliminate errors.

y = -22 + -4

When we add two negatives together, the sum is a larger negative

y = -26

Answer 2

-2x + x-4 = 18

-x-4 =18

-x = 22

x=-22 ---> y = -22-4 = -26