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Published byJordan Purcell Modified over 2 years ago

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Angles In Triangles Types of Triangles Equilateral Triangle 3 equal sides 3 equal angles. Isosceles triangle 2 equal sides 2 equal angles (base) Scalene triangle 3 unequal sides 3 unequal angles

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Any triangle containing a 90 o 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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To determine the angle sum of any Triangle Take 3 indentical copies of this triangle like so: How can we use this to help us? Angles on a straight line add to 180 o These are the same angles as in the triangle! The angle sum of a triangle = 180 0

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

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

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

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