先化简,再求值1/x-1+3/2-x-x的平方,其中X=-5/2

问题描述:

先化简,再求值1/x-1+3/2-x-x的平方,其中X=-5/2

解:
1/x-1+3/2-x-x的平方
=1/(x-1)+3/(2-x-x^2)
=(x+2)/(x+2)(x-1)-3/(x+2)(x-1)
=(x+2-3)/(x+2)(x-1)
=(x-1)/(x+2)(x-1)
=1/(x+2)
当x=-5/2,
原式=1/(-5/2+2)
=1/(-1/2)
=-2