先化简再求值a-2/a+3÷a平方-4/2a+6-5/a+2

(a-2)/(a+3) ÷ (a^2-4)/(2a+6) - 5/(a+2)= (a-2)/(a+3) * (2a+6) / (a^2-4) - 5/(a+2)= (a-2)/(a+3) * 2(a+3) / {(a+2)(a-2)} - 5/(a+2)=2 / (a+2) - 5/(a+2)= - 3/(a+2)