y=-2x-6 y=3x+6

Question

substitution

Answer 1

Since y is both expressions, then the expressions are equal to one another:

Substituting for y: -2x-6=3x+6; subtract 6 from each side: -2x-12=3x;

add 2x to each side: -12=5x or 5x=-12 so x=-12/5 or -2.4 or -2 2/5.

So, substituting for x, y=-2x-6=4.8-6=-1.2 or y=3x+6=-7.2+6=-1.2, the same value (y=24/5-6=(24-30)/5=-6/5=-1.2).

x=-12/5 or -2.4; y=-6/5 or -1.2 (or -1 1/5).

Another way to the solution is to add the equations together: 2y=x then substitute for x: y=-4y-6, so 5y=-6 and y=-6/5 or -1.2. So substituting for y in either equation: -6/5=-2x-6; 6-6/5=-2x; (30-6)/5=-2x; -2x=24/5; x=-12/5 or -2.4. Or, since 2y=x, x=2*(-6/5)=-12/5.