I am currently doing some exercise on the Lagrange multipliers methods and have come upon some confusion. following my lectures notes is says:
$$L= f(x,y) + \lambda g(x,y) $$
and in some online examples it says:
$$L= f(x,y) - \lambda g(x,y) $$
where $f(x,y)$ is the function to be minimized/maximized and $g(x,y)$ is the constraint.
Which one is correct? many thanks