坐標幾何

If $d$ is the distance between the point $(a,b)$ and $(b,a)$, then $d^2=$

In the figure, the equation of the straight line is $y=mx+c$. Which one of the following is true?

If $\begin{cases}x\ge0,\\ y\ge0,\\ x+y\le5,\\ 2x+y\ge4,\\ x\ge y,\end{cases}$ in which of the following shaded regions do all the points satisfy the above inequalities?

In the figure, which point in the shaded region will make the value of $x-2y$ a minimum?