Solving System of Equations

By Substituion

Two equations together are called a system of equations.

Example 1:

y = 4x

3x + 3y = -14

Substitute y = 4x for y in the second equation:

3x + 3(4x) = -14

3x + 12 x = 15x = -14

x = - 14/15; y = -56/15

Example 2:

x + 2y = 4

4x - 2y = 8

Solve for y in equation 1.

y = (4 - x)/2

Substitute for y in the second equation:

4x - 2( (4 - x)/2 ) = 8

 4x - 8/2 + 2x/2 = 8

4x - 4 + x= 8

5x = 8 +4 =  12

x = 2.4; y = 0.8

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