Use the method of substitution to solve the system of linear equations.

Question

4x-y=3

9x-2y=8

The solution is (In an ordered pair)

Answer 1

First solve one of the equations for y

4x-y=3

-y=3-4x

y=-3+4x

then substitute -3+4x for y in the other equation.

9x-2(-3+4x)=8

9x+6-8x=8

x+6=8

x=2

substitute 2 for x in either equation and solve for y

9(2)-2y=8

18-2y=8

-2y=-10

y=5

check--

4(2)-5= 3

8-5=3

and

9(2)-2(5)=8

18-10=8

8=8

 

 

Answer 2

Solve for any variable from either equation:

(1) 4x - y = 3  ==> y = 4x - 3

Substitute into other equation:

(2) 9x - 2y = 8

9x - 2(4x - 3) = 8

Solve:

9x - 8x + 6 = 8

x + 6 = 8

x = 2

Substitute to find y:

y = 4x - 3 = 4(2) - 3

y = 8 - 3 = 5