F(x)应该是A+Be^(-2x)吧1，X连续，所以F(0)=0得到A+B=0然后F(+∞) = 1所以A=1所以B=-12，P(03,f(x) = F'(x) = 2e^(-2x) x>0f(x) = 0, x≤0
