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Published byJordan Purcell Modified over 5 years ago

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**Angles In Triangles Types of Triangles Isosceles triangle**

2 equal sides 2 equal angles (base) Equilateral Triangle 3 equal sides 3 equal angles. Scalene triangle 3 unequal sides 3 unequal angles

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**Any triangle containing a 90o angle is a right-angled triangle**

An isosceles or a scalene triangle may contain a right angle. Right-angled isosceles triangles. Right-angled scalene triangle.

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**The angle sum of a triangle = 1800**

To determine the angle sum of any Triangle How can we use this to help us? Take 3 indentical copies of this triangle like so: 3 1 2 Angles on a straight line add to 180o These are the same angles as in the triangle! The angle sum of a triangle = 1800

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**Calculate angles a, b and c**

Calculating unknown Angles Example 1 a 65o Calculate angle a. Angle a = 180 – ( ) = 180 – 155 = 25o Example 2 Calculate angles a, b and c a b c Since the triangle is equilateral, angles a, b and c are all 60o (180/3)

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**Calculating unknown Angles**

Example 3 a 65o Calculate angle a. b Angle a = 65o (base angles of an isosceles triangle are equal). Angle b = 180 –( ) = 180 – 130 = 50o Example 4 Calculate angles x and y y 130o x

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**Calculate angles a and b.**

Calculating unknown Angles Example 5 Calculate angles a and b. b a Example 6 Calculate angle a 15o 27o a Angle a = 180 – ( ) = 180 – 42 = 138o

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