What is the area of the region bounded by |x| <= 2k and |y| <= k where k is a positive real number?

Under what condition will the lines $m{}^{2}x+ny-1=0$ and $n{}^{2}x-my+2=0$ be perpendicular?

If p and q are real numbers between 0 and 1 such that the points (p,1), (1,q) and (0,0) form an equilateral triangle, then what is $(p+q)$ equal to?

Let A(3, -1) and B(1, 1) be the end points of line segment AB. Let P be the middle point of the line segment AB. Let Q be the point situated at a distance $\sqrt{2}$ units from P on the perpendicular bisector line of AB. What are the possible coordinates of Q?