a= 2/3,则a²-2a-3/a²-7a+12 的值等于________.

题目

a= 2/3,则a²-2a-3/a²-7a+12 的值等于________.

答案

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