(x²-1)/(x²+2x+1)-(x+1)/(x-1)
=(x+1)(x-1)/(x+1)²-(x+1)/(x-1)
=(x-1)/(x+1)-(x+1)/(x-1)
=[(x-1)²-(x+1)²]/[(x+1)(x-1)]
=(-4x)/(x²-1)
当x=0时,原式=0等腰三角形的顶角为100度,则它腰上的高与底边的夹角是50°若9x的平方-KXY+4y的平方是一个完全平方式，则k的值是12或者-12