GEOMETRY QUICK GUIDE 1: ANGLES

Name

Date

GEOMETRY QUICK GUIDE 1: ANGLES

Angle Types

Angle Rules

Acute angle < 90?

a

b

Angles in a triangle add up to

180?

c

So a + b + c = 180?

Angles on a straight line add up to 180?

So a + b = 180?

Right angle = 90?

Angles in a quadrilateral add up to 360?.

So a + b + c + d = 360?

Obtuse angle > 90? and < 180?

Straight line = 180?

Reflex angle > 180?

Angles around a point add up to 360?.

So a + b + c + d + e = 360?

Angles in regular shapes

Name of shape equilateral triangle

square regular pentagon regular hexagon regular heptagon regular octagon regular nonagon regular decagon

Sides 3 4 5 6 7 8 9 10

Interior angles 60? 90? 108? 120?

128.6? 135? 140? 144?

Sum of Interior angles of regular n-sided polygons is 180(n-2)?. To find the interior angle, divide this amount by the number of sides, n.

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