∫[0：θ] [x·n(θ-x)ⁿ⁻¹/θⁿ]dx=-(1/θⁿ)∫[0：θ]xd[(θ-x)ⁿ]=-(1/θⁿ)x(θ-x)ⁿ|[0：θ]+(1/θⁿ)∫[0：θ](θ-x)ⁿdx=(1/θⁿ)[0·(θ-0)ⁿ-θ·(θ-θ)ⁿ]-[1/ (n+1)θⁿ](θ-x)ⁿ⁺¹|[0：θ]=[1/ (n+1)θⁿ][(θ-0)ⁿ⁺¹-(θ-θ)ⁿ⁺¹]=θ/(n+1)
