M1 Maths Exponential Functions

做左a題..唔識做b題=(
(a) Express each of the following as an infinite series.
(i)e = 2+1/2+1/6+1/24+...+1/(r!)+...
(ii)e^(-1) = 1/2-1/6+1/24-...+(-1)^(r)/(r!)+...

圖片參考：http://imgcld.yimg.com/8/n/HA00967484/o/701102090101313873378810.jpg


Answer for (b): 1/2{e+e^(-1)}