1/2+1-1/(n+1)-1/(n+2)怎么化简解：1/2+1-1/(n+1)-1/(n+2)=3/2-(n+2+n+1)/[(n+1)(n+2)]=3/2-(2n+3)/(n²+3n+2)=(3n²+9n+6-4n-6)/(2n²+6n+4)=(3n²+5n)/(2n²+6n+4)
