The values of x are 2 and -1.
Solving the equation created by substitution listed in the question:
-2x+14=x²-3x+12
Add 2x to both sides:
-2x+14+2x=x²-3x+12+2x
14=x²-1x+12
Subtract 14 from both sides:
14-14=x²-1x+12-14
0=x²-1x-2
Factoring this, we want factors of -2 that sum to -1; -2(1) = -2 and -2+1=-1:
0=(x-2)(x+1)
Using the zero product property, we know that either x-2=0 or x+1=0:
x-2=0
x-2+2=0+2
x=2
x+1=0
x+1-1=0-1
x=-1