P(-2≤X≤0)=P(-2/σ≤X/σ≤0)=F(0)-F(-2/σ)=F(0)+F(2/σ)-1=0.4
所以F(2/σ)=0.9 查表得2/σ=1.285 σ=1.556
P(X>2)=1-P(X