how would you substitute x=-4y and 3x + 2y = 20

Question

I need help on a really hard problem it's substitution equations

 

Answer 1

Substitute  x=-4y  into   3x+2y=20.

 

 

3(-4y) + 2y = 20

 

 

This will allow you to solve for y.  Then substitute that value of y into the first equation to solve for x.

Answer 2

Hi Ricky!

 

Given  3x + 2y = 20         

      and x=-4y,

 

Substitute x in the first equation into x=-4y. The first equation will then become....

 

         3(-4y) + 2y = 20

 

 

        -12y + 2y   = 20            Combine similar terms.

 

          -10 y   = 20

 

          -10 y/-10   = 20/-10

 

              y = -2

 

 

Now that we know the value of y, solve for x in terms of y.

 

             x =-4y

             x = -4 (-2)

 

            x = 8

 

 

Hope that helps.