“To solve a system of equations by substitution”

means to solve the unknown values of two equations by substituting.

1) Find the values of x and y

3x+4y=-4

x+2y=2

x+2y–2y=2–2y

=> To remove all the other things other than x from the left side, subtract 2y from both sides.

x=2–2y

=> Then you get this. Now you are ready to substitute this into the other equation.

3x+4y=-4

=> Substitute x= 2 –2y for x.

3(2 – 2y)+4y=-4

=> Simplify this equation.

6-6y+4y=-4

-2y=-10

y=5

=> Substitute this for one of the equations.

3x+4(5)=-4

=> Simplify.

3x+20=-4

3x=-24

x=-8

x=-8, y=5

=>This is the answer you should get.

2) Example Problems

· 2x+3y=5, x-5y=9

· x+2y=2, 7x-3y=-20

· 3x-y=4, 5x+3y=9