I agree that the point $(2,2)$, is the only one that meets all criteria. Now we need to compare the value of $f$ at another point on the constraint,...
There is an unclosed curly brace after method has12, but an extra closing brace after method linearIn. Also, you have not addressed by remark 2 from...
What I would do is observe that we have cyclical symmetry, that is we may interchange $x_1$ and $x_2$ with no change in either the objective function...