Question

先化简,在求值.（1/a+2-1）a2-1/a+2,其中a =3

Answer 1

原式=[1/(a+2) -(a+2)/(a+2)] ÷(a+1)(a-1)/(a+2)

=[1-(a+2)]/(a+2) ×(a+2)/(a+1)(a-1)

=-(a+1)/(a+1)(a-1)

=-1/(a-1)

当a=3时

原式=-1/(3-1)

=-1/2