设函数u=F(x,y,z)在条件φ(x,y,z )=0和ψ(x,y,z )=0下在点(x0,y0,z0 )取得极值

u=F(x,y,z)在点(x0,y0,z0 )取到极值,必然满足存在两个数λ1,λ2,使得P(x,y,z)=F(x,y,z)+λ1φ(x,y,z)+λ2ψ(x,y,z)在φ(x0,y0,z0)=0,ψ(x0,y0,z0)=0的条件下满足P'x(x0,y0,z0)=F'x(x0,y0,z0)+λ1φ'x(x0,y0,z0)+λ2...