Question

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

Answer 1

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`