The easiest way to tell which is the answer is to quickly
mentally substitute x=0 in 2x^2-2x+7, which easily gives +7.
Then we quickly mentally substituting x=0 in each of the choices:
a) (4x+12)+(2x^2-6x+5)
Substituting x=0 mentally in that gives 12+5 or 17, thus it
cannot be the correct choice.
b) (x^2-5x+13)+(x^2+3x-6)
Substituting x=0 mentally in that gives 13-6 or +7, thus it
is a possible choice.
c) (4x^2-6x+11)+(2x^2-4x+4)
Substituting x=0 mentally in that gives 11+4 or 15, thus it
cannot be the correct choice.
d) (5x^2-8x+120)+(-3x^2+10x-13)
Substituting x=0 mentally in that gives 120-13 or 107, thus it
cannot be the correct choice.
So the answer is (b), the only one that gave +7 when 0 was
mentally substituted for x. This is much easier than simplifying
each one to see which simplifies to the same. If more than one
choice had given +7 when x was substituted for x, I would then
have also mentally substituted x=1 in those.
Edwin
