1. Angle. It is the figure formed by two rays, called the sides of the angle.
The angle of the upper drawing has two sides BC and BA.
The origin of the two rays is the vertex B.
This angle is read ABC, mentioning the vertex in the middle.
2. The right angle
In the left figure, there are two angles: ABC and CBD, the sum of them is ABD. The two angles are acute.
In the right figure, we see two lines CD and EF intersect at point O. In this case the two lines are perpendicular and form four right angles as the EOD. The acute angle is less than the right angle.
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