to find angles in special triangles

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Presentation transcript:

to find angles in special triangles Triangles and Quadrilaterals Objectives: to find angles in special triangles To calculate the degrees in a quadrilateral

What do you notice about the angles in a triangle? A straight line Allow 10 minutes for this activity esp giving out paper, issuing scissors and checking classwork. What do you notice about the angles in a triangle?

? 30° To find the missing angle 180° – (sum of given angles) = ? Angles in a Triangle always add up to 180° ? 70° 30° To find the missing angle 180° – (sum of given angles) = ? Copy this diagram and rule into your books – allow 3 minutes. 180° - 70°- 30° = 80°

Find the missing angles a, b, c and d. 30° 45° 20° a 60° b 63° 29° Sketch diagrams – not accurate but with a ruler pls - and answers with workings allow 10 minutes. NB Right angle notation. c 72° d

Equilateral Triangle The angles are always 60° All angles are equal. All Sides are equal The angles are always 60°

Isoceles Triangle 2 angles are equal. 2 Sides are equal

Right – Angled Triangle 1 angle always 90° 2 other angles = 90°

Scalene Triangle No Equal Sides No Equal angles

Find the missing angles b 80̊ a 120̊ Sketch diagrams – not accurate but with a ruler pls - and answers with workings allow 10 minutes. NB Right angle notation. c d 30̊

Can you work out the missing angle a? Plenary……Finding missing angles using 2 x angle facts - GCSE Grade “E” Skill

What do all of these shapes have in common? Plenary……Finding missing angles using 2 x angle facts - GCSE Grade “E” Skill

Can you work out the missing angle b? 115 ̊ 115 ̊ Plenary……Finding missing angles using 2 x angle facts - GCSE Grade “E” Skill 65 ̊

Odd one out? 40, 40, 140 50, 50, 80 30, 40, 110 35, 45, 90 60, 60, 60 100, 20, 70

1. Triangles can have more than 1 obtuse angle Sometimes, Always, Never 1. Triangles can have more than 1 obtuse angle 2. A right angled triangle can also be an isoceles angle 3. A triangle with a 60º angle is an equilateral 4. There are two triangles in all 4 sided shapes