The purple squares are all the same size. I’ve arranged three of them symmetrically inside each of the two black squares. What’s the missing length?
Let be the side length of one of the purple squares. So and both have length . The diagonal of the square is then , so that is the length of . Let be the length of , then this is also the length of . Then the width of the square is and the height is . As it is a square, these are both equal to . The length requested is which can be seen to be equal to: