How do you solve the following system: x-5y=-9, y = 3x – 12?

1 Answer
Mar 26, 2018

You have to substitute (replace) one of the unknowns into the other equation

Explanation:

We know that x-5y=-9, so from here we have:

x=5y-9. Substituting in the other equation we have:

y=3x-12=3(5y-9)-12=15y-27-12=15y-39, and then:

y+39=15y, and so 39=14y, and then y=39/14

We can now use that x=5y-9, so we have x=5*39/14-9=195/14-9=(195-126)/14=69/14

The solutions are then x=69/14, y = 39/14