(P(neg)=((erfc[-(1/(Sqrt[2]))(((Subscript[v, 0])/σ)-C σ)])/(erfc[-(1/(Sqrt[2]))(((Subscript[v, 0])/σ))]))(e^(-(Subscript[Cv, 0])+(1/2)(σ^2)(C^2)))
As   erfc(z)=(∫_z^∞)(2/(Sqrt[π])) (e^(-(t^2)))dt
So   ((d )/dz)erfc(z)=-(2/(Sqrt[π]))(e^(-(z^2)))
Hence,((d )/dC)erfc[-(1/2)(((Subscript[v, 0])/σ)-C σ)]=-(2/(Sqrt[π]))(e^(-(((((Subscript[v, 0])/σ)-C σ))^2)))(σ/(Sqrt[2]))(7))