Here we will discuss about the sign of angles before that let us recall in brief the definition of an angle.
What is an angle?
An angle is made up of two rays with a common end point. This end point is the vertex of the angle.
Here, in the above figure the angle is named as ∠ABC or ∠B.
The definition of an angle is very useful in geometry. In Trigonometry, we need a detailed definition of an angle.
Let a revolving line starting from OX, rotate about O in a plane and stop at position OP. Then it is said to trace out an angle XOP. OX is called initial side, OP is final or terminal side and O is the vertex of the angle. If rotation is anticlockwise, the angle is positive. If rotation is clock-wise, the angle is negative.
An angle is said to lie in a particular quadrant if the terminal side of an angle lie in the quadrant.`
● Measurement of Angles