If the vertices Band D of a square ABCD are (2, 3) and (4, 1) respectively, then what is the area of the square?

What is the value of sin $\theta $ if $\theta $ is the acute angle between the lines whose equations are px + qy = p + q and p(x - y) + q(x + y) = 2q 

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?