用平方差公式
原式
=(100²=99²)+(98²-97²)+.+(2²-1²)
=100+99+98+97+...+2+1
=100(100+1)/2
=5050(a+b)(a-b)-2(a²-5b²)=(x+2)(x+4)+x²-4=x²-y²+2x-2y=(a+b)(a-b)-2(a²-5b²)=a²-b²-2a²+10b²=9b²-a²=(3b+a)(3b-a)(x+2)(x+4)+x²-4=(x+2)(x+4)+(x+2)(x-2)=(x+2)(x+4+x-2)=2(x+2)(x+1)x²-y²+2x-2y=(x+y)(x-y)+2(x-y)=(x-y)(x+y+2)已知X²-Y²=-1，X+Y=½，求x-y的值。已知n为整数，说明（n+7)-(n-3)²的值一定能被20整除。（x²-y²)-x²y²=a²-1与a²-3ad的公因式是？x²-y²=(x+y)(x-y)=(x-y)*1/2=-1∴x-y=-2后两个你都写错了吧，认真点儿