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Properties of Triangles

Properties of Triangles. Objectives: G Grade Identify isosceles, equilateral and right-angled triangles. Use the word ‘congruent’ when triangles are identical. E Grade Show that the angles of a triangle add up to 180 o and use this to find angles.

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Properties of Triangles

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  1. Properties of Triangles Objectives: G Grade Identify isosceles, equilateral and right-angled triangles. Use the word ‘congruent’ when triangles are identical. E Grade Show that the angles of a triangle add up to 180o and use this to find angles. Show that the exterior angle of a triangle is equal to the sum of the interior opposite angles. Use angle properties of isosceles, equilateral and right-angled triangles.

  2. Properties of Triangles C c b a A B When a side of a polygon is extended an exterior angle is created We know that the sum of internal angles (a + b + c) = 180o We also know that angles on a line add up to 180o Therefore if: a + c + b = 180o and b + external angle = 180o The external angle = a + c

  3. Properties of Triangles Example y y x is an exterior angle so x = 39 + 81 = 120o x x x x is again an exterior angle so 81o 81o 39o 39o 120 = y + 90 so y = 30o

  4. Properties of Triangles Now do these: c = 63 + 74 = 137o d = 180 - 63 = 113o e = 180 - 74 = 106o a = 42 + 40 = 82o b = 138 - 48 = 90o 132 = x + 90 x = 42o

  5. Properties of Triangles Now do these: r = 140 - 32 = 108o 180 - 140 = 40o p = 49 + 63 = 112o 180 - 118 = 62o q = 49 + 76 = 125o s = 180 – (40 + 62) = 78o Bearing 131 + 180 =311o or 270 + 41 =311o x = 131 - 90 = 41o

  6. Properties of Triangles Worksheet

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