Question

8x–2y=4 4x+5y=–18 How do you solve using the substitution method?

Answer 1

First we'll need to isolate one of the variables. Lets start with the equation 8x - 2y = 4

8x - 2y = 4

Lets subtract 8x from both sides:

-2y = 4 - 8x

Now we'll divide both sides by -2:

y = -2 + 4x

Now we have the (y) variable isolated in terms of (x), so lets substitute our equation in for (y) in the second equation:

4x + 5y = -18

We found out that y = -2 + 4x, so lets plug that in for the (y) above:

4x + 5( -2 + 4x ) = -18

4x - 10 + 20x = -18

24x = 18

x = 3/4

Now that we know what (x) equals to, lets plug into our equation y = -2 + 4x to find out (y):

y = -2 + 4x

y = -2 + 4( 3/4)

y = -2 + 3

y = 1

so x =3/4 and y =1