(9又9分之1+1又8分之7-5又7分之6)÷(9又9分之1-6又7分之6+2又8分之7)
=(9+1/9+2-1/8-6+1/7)/(9+1/9-7+1/7+3-1/8)
=(5+1/9+1/7-1/8)/(5+1/9+1/7-1/8)
=1