fk(x)=P(Ck∣x) or equivalently, fk(x)=P(x∣Ck)P(Ck)f_k(x) = P(C_k|x) \; or \; equivalently, \; f_k(x) = P(x|C_k) P(C_k)fk(x)=P(Ck∣x)orequivalently,fk(x)=P(x∣Ck)P(Ck)