2x^4-3x^3+ax^2+7x+b=(2x^2+mx+n)(x^2+x-2)
=2x^4+(m+2)x^3+(-4+m+n)x^2+(-2m+n)x-2n
m+2=-3
-4+m+n=a
-2m+n=7
-2n=b
m+2=-3
-2m+n=7
m=-5,n=-3
a=-4+m+n=-12
b=-2n=6

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