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.