(2x的2次方+6x+1)(x的2次方+3x-2)-18=[2(x的2次方+3x)+1][(x的2次方+3x)-2]-18令x²+3x=t原式=(2t+1)(t-2)-18=2t²-3t-2-18=2t²-3t-20=(2t+5)(t-4)将x²+3x=t还原得(2x²+6x+5)(x²+3x-4)=...