It is easy to find out that right triangle is only half of the square. And again there is a rectangle with a triangle shaded in red color. The red triangle is half the area of the rectangle. But to calculate just the area of triangle, we can calculate the area of the rectangle whose area is length times width. When we have a rectangle with its length and width as 4u and 2u respectively then the area of that rectangle will be equal to 8u(squared). But we already know that the triangle is half of the rectangle so we need to count only half the rectangle. So when 4 times 2 is divided by 2 then we will have 4 and the are of the right triangle will be 4u(square). With this we get to find the area of the right triangle easily.