若a=2/3,则aa-2a-3/aa-7a+12的值等于

问题描述:

若a=2/3,则aa-2a-3/aa-7a+12的值等于

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