Hi everybody. Given is a function f(x,y). Sought is a point Px/Py on f(x,y)=1, whose tangent is perpendicular to the vektor n=(1,0). Without any reference to the specific function in the solution it is stated, that grad(Px/Py)=\lambda*n=1,0.

1) why is this generally true?

(If needed, the specific function is f(x,y)=3{x}^{2} +xln(y)+{e}^{ax} , x1≥0,x2>0,a∈R.)

Thanks for your help

Alex

(sry latex smhw doesnt work with me; \lambda* just means vector n multiplied with a random number