x的4方+4x的3方-2mx²-2x²+nx³-2x+3
=x的4方+(4+n)x³-(2m+2)x²-2x+3
不含x²和x³
则4+n=0,n=-4
2m+2=0,m=-1
4n²-5mn-7
=4×16-20-7
=37