若a=三分之二,则（分数）a平方-7a+12分之a平方-2a-3的值等于,_数学解答

若a=三分之二,则（分数）a平方-7a+12分之a平方-2a-3的值等于,

人气：286 ℃　时间：2020-05-29 05:37:54

解答

(a²-2a-3)/(a²-7a+12)
=(a-3)(a+1)/(a-3)/(a-4)
=(a+1)/(a-4)
=(2/3+1)/(2/3-4)
=5/3/(-10/3)
=5/3*(-3/10)
=-1/2