Thanks. That is one rectangle only, for explanation only I created diagonals, and mid lines( vertical, horizondal). I cannot use calculator(this is for my project , programatically i need), I need a formula to get angle in degrees. please explain to get all angles of diagonals from the mid point.( theta1 to theta8)
it doesn't matter which rectangle you use because all marked rectangles are similar to the complete rectangle. (see attachment)
By law of symmetry you can proof that
But I can't help you with the exact value of the angle because I don't know the measures of the rectangle.