d u-p 高斯(标准)正态分布 x-4F(U)= a√2z/ewp/-y Idx 2 P(x2u)=1-P(x <u)=1-pl u-ll when: u=u-20 Pxsl)=-/=/4-2a-=(-2)=2275% P(x≥a)=1-dp(-2)=(2)=97725%      −   u  高斯（标准）正态分布  −  = x y ( )   −       = − dx y F y 2 exp 2 1 2   ( ) ( )       −  = −  = −  u  P x u 1 P x u 1 P(x  u) =       −   u        − − =    2  when :u =  − 2 = (−2) = 2.275% P(x  u) = 1−(−2) = (2)= 97.725%