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?

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?