In this video I will explain how mathematicians approximated the constant e=2.7182818284590... They used the infinite series of e^x=1+(x/1!)+(x^2/2!)+(x^3/3!)+(x^4/4!)+..., and when they let x=1 then they will get e^1=e=1+(1/1)+(1/2)+(1/6)+(1/24)+(1/120)+...