solve by the substitute method
5x+5y=5
-9x+y=31

Question

anonymous · Answer

You have the two equations
  
  5x + 5y = 5
  y - 9x = 31

You would one to use the second equation because there is a coefficient of 1 for y, which simplify the substitution method.

y - 9x = 31        Move everything over from the side where y is.
y = 9x + 31

Take our first equation and plug our re-arranged equation in to y

5x + 5y = 5
5x + 5(9x + 31) = 5     Multiply 5 to what is inside the parenthesis
5x + 45x + 155 = 5     Combine like terms
50x + 155 = 5             Subtract 155 on both sides
50x = -150                   Divide by 50 on both sides
x = -3

We now need to take one of the equations and plug -3 in for x; it doesn't matter which equation it is, so we will use the first one.

5x + 5y = 5               Plug in -3 for x
5(-3) + 5y = 5           Multiply
-15 + 5y = 5              Add 15 on both sides
5y = 20                      Divide by 5 on both sides
y = 4

x is equal to -3 and y is equal to 4