Right angle
A right angle is an angle of 90 degrees. If you draw the straight line and an another one that crosses it, in such the way that all angles have the same size, the result is the picture with four right angles. The top of the letter T is at right angles to the vertical line. Walls of buildings are usually at right angles to the floor. Two things that are at right angles are called "perpendicular".
A simple right angle can be made by folding the piece of paper twice. guided tour test