1993²-1992×1994
=1993²-(1993-1)×(1993+1)
=1993²-(1993²-1²)
=1993²-1993²+1²
=1分解因式：-3分之二x的5次方+4x的4次方-6x的3次方？-2/3x^5+4x^4-6x^3 =-2/3x^3(x²-6x+9) =-2/3x^3(x-3)²