4/4号面试。

1. integral lnx/x
2. integral x^x^2
3. pdf for normal distribution and exponential distribution. sigma and miu for normal and standard normal distribution.
4. put call parity.
5. Taylor polynomial 2nd order f(x,y)=xsinx
6. a european option is 5 dollars. how about americcan option with same strike price and maturity.