Solve using substitution

Question

2x-y=5

-2x-5y=11

Answer 1

Equation 1:  2x - y = 5

Equation 2:  -2x - 5y = 11

 

Get y from equation 1:

 

y = 2x - 5

 

Substitute this y in equation 2, then solve for x:

 

-2x -5(2x - 5) = 11

-2x -10x + 25 = 11

-12x = 11 - 25

-12x = -14

x = 14/12 = 7/6

 

Substitute this x back into y = 2x - 5 and solve for y:

 

y = 2(7/6) - 5 = (14 - 30) / 6 = -16/6 = -8/3

 

You can now test the answers by substituting them back into equations 1 and 2:

 

2(7/6) - (-8/3) = 14/6 + 8/3 = (14 + 16) / 6 = 30/6 = 5

-2(7/6) - 5(-8/3) = -14/6 + 40/3 = (-14 + 80) / 6 = 66/6 = 11