Theory:

Angle bisector:
A line, line segment or ray that divides the angle into two equal angles is the angle bisector.
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Incentre:
The point of concurrence of the three angle bisectors of the triangle is the incentre of the triangle.
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Whyis it called the incentre?
 
With the incentre as the centre, we can construct a circle such that the circle touches all three sides of the triangle internally.
 
Consider the figure given below for a better understanding.
 
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