If we look carefully at the floor, walls and ceiling of any building then we see a particular inclination in the corners of floor, walls and ceiling.
See carefully the hour and minute hands of a clock at 3 o’clock and 9 o’clock. We found that they are in the same position with each other as we have seen the inclination walls and floor. This particular inclination is known as right angle. Therefore, such an angle between two planes or lines is known as right angle. It is expressed by
