Angles: When two straight lines meet at a point they form an angle. In the figure, the angle is represented as ∠AOB. OA and OB are the arms of ∠AOB. Point O is the vertex of ∠AOB. The amount of turning from one arm (OA) to other (OB) is called the measure of the angle (AOB).
Right angle: An angle whose measure is 90° is called a right angle. ∠BOA is a right angle in the figure.
Acute angle: An angle whose measure is less then one right angle (i.e., less than 90°), is called an acute angle.
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A triangle is a three sided closed figure·
A triangle whose all the sides are unequal is called a scalene triangle. All the three angles will also be different in this case.
AB ¹ BC ¹ AC
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Incentre is concurrence point of angle bisectors of triangle. The three sides of the triangle are tangents to the cirle with centre O.
Radius of in circle of an equilateral triangle of side a = a/2Ö3
op = oq = or = radius or Inradius and o is incentre
· Circum centre is concurrence point of perpendicular bisectors of a triangle.
