Let $k$ be a real number between $0$ and $1$.
What is the area of the quadrilateral formed by the lines $y = kx, y = kx + 1, x = ky$ and $x = ky + 1$?
I tried replacing $k$ with $0.5$, however it was hard to convert back. So what is an easy method that I can use to solve this problem? The method I used is so long. I tried graphing, however it is just a parallelogram.