Drag the points AND HAVE FUNNNNN!! Blue is original triangle and black is rotated triangle.
Used the rotation method, possible invented by me, or replicated by coincidence. So basically what it does is that it finds the direction of a select line , then takes the coordinates of the triangle when turned in that direction clockwise. From this point on you can use the formula Area=Base*Height*1/2, since now the base is flat and the height is easy to calculate.