Question

化简求值：已知1+1/a=3.求[（a^2-5/a-1)+1]×(a^2-1/a^2-2a)÷(a+3)=

Answer 1

1+1/a=3,a=1/2 将a=1/2代入式子得：[（(1/2)^2-5/(1/2-1))+1]×((1/2)^2-1/(1/2)^2-2*(1/2))÷(1/2+3) = [1/4-10]*(1/4-8)÷7/2 =39/31*2/7 =78/217