Question

谁知道第二、三题的第一步是否正确？我用计算器算了，和答案不一样啊！！！

Answer 1

(2)
11+ (22+1/2)+(33+1/4)+....+(77+1/64)
=(11+22+33+...+77) +(1/2+1/4+...+1/64)
=(11+77)x(7/2) + (1/2)( 1 - (1/2)^6)/(1-1/2)
=308 + 1 - 1/64
=308 + 63/64
=308又64分之63
(3)

1+(3+1/6)+(5+1/12)+...+(17+1/90)
=(1+3+5+...+17) +(1/6+1/12+...+1/90)
=(1+3+5+...+17) +[1/(2x3)+1/(3x4)+...+1/(9x10) ]
=(1+17)x(9/2) + [ (1/2-1/3)+(1/3-1/4)+...+(1/9-1/10) ]
=81 + 1/2 -1/10
=81 + 2/5
=81又 5分之2