Question

f g may be replaced by f + g) where is a lagrange multiplier

Answer 1

When you want to maximize (or minimize) a multivariable function \blueE{f(x, y, \dots)}f(x,y,…) subject to the constraint that another multivariable function equals a constant, \redE{g(x, y, \dots) = c}g(x,y,…)=c

I thick this.....