应该是7/12不是8/121/3-7/12+9/20-11/30+13/42-15/56=1/3-(3+4)/12+(4+5)/20-(5+6)/30+(6+7)/42-(7+8)/56=1/3-1/3-1/4+1/4+1/5-1/5-1/6+1/6+1/7-1/7-1/8=-1/8原式=(1/3-8/12+9/20-11/30+13/42-15/56)*2^3-(-2）^100*...