原式=[ 1- 1/(a+1) ]- [ a/(a²+2a+1) ]=1 - 1/(a+1) - a/(a+1)²=(a+1)²/(a+1)² - (a+1)/(a+1)² -a/(a+1)²=[ (a+1)²-(a+1) -a ]/(a+1)²=(a²+2a+1-a-1-a)/(a+1)²=a...