1、 先化简再求值.1/(x-1)+3/(2-x-x平方).其中x=-5/2.2、若 x-3/[(x+1)(x-1)]=A/(x+1)+B/(x-1) .求AB的值.

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1、 先化简再求值.1/(x-1)+3/(2-x-x平方).其中x=-5/2.
2、若 x-3/[(x+1)(x-1)]=A/(x+1)+B/(x-1) .求AB的值.


(1)原式=(x+2)/(X-1)(X+2)-3/(X-1)(X+2)
=1/(X+2);又x=-5/2
所以=-2
(2)由题,右边分母有理化可得
x-3=(A+B)x-(A-B)所以a-b=3;a+b=i
a=2,b=-1
所以AB=-2
(手打,求采纳)

1:=1/x-1 -3/(x-1)(x+2)=1/(x+2) 再带入计算
2:得:x-3=(A+B)x+(B-A) 所以:A+B=1 A-B=3 得 A=2 B=-1

1)1/(x-1)+3/(2-x-x平方)=1/(x-1)-3/(x平方+x-2)=1/(x-1)+3/(x-1)(x+2)=(x+2-3)/(x-1)(x+2)
=1/(x+2) =-2
2)x-3/[(x+1)(x-1)]=A/(x+1)+B/(x-1) x-3/[(x+1)(x-1)]=[A(x-1)+B(x+1)]/(x+1)(x-1) =[(A+B)x+(-A+B)]/(x+1)(x-1) A+B=1 -A+B=-3 A=2 B=-1 AB=-2