How do you solve the system y=5x-7 y=5x7 and -3x-2y=-123x2y=12 by substitution?

1 Answer
Jun 3, 2015

We know that y=5x-7y=5x7 so we are just going to replace the yy in the other equation :

-3x-2y=-123x2y=12
-3x-2*(5x-7)=-123x2(5x7)=12
-3x-10x+14=-123x10x+14=12
-13x=-12-1413x=1214 ( we substract 1414 on each side )
-13x=-2613x=26
x=2x=2 ( we divide by -1313 on each side )

Now that we have xx, we can find yy with the first equation :

y=5x-7y=5x7
y=5*2-7y=527
y=10-7y=107
y=3y=3