Angles in a straight Angles in a straight line and around a line and around a

pointpoint

Angles in a straight Angles in a straight line and around a line and around a

pointpoint

Lesson Objectives• To understand the sum of angles

in a straight line• To understand the sum of angles

around a point• To be able to answer questions by

using these two rule to find unknown angles.

What angle is this?

=90°

A right-angle

If there are 90° in a right-angle, how many are

their in a straight line?

90°90°

90°+90°=

180°

As there are 180° in a straight line, what is the

unknown angle here?

45°

?

180°- 45° =

135°

135°

If the angles in a straight line equal 180°, what do the angles around a point

add up to?90°90°

90° 90°

90°+90°+90°+90°=

360°

As there are 360° around a point, what is the unknown

angle here?

45°

60°45°100°

?

360° - 45° - 60° - 45° - 100° =

110°

110°

Copy out the following definitions:

Angles in a straight line = 180°

45°

?

180°- 45° =135°

45°

60°45°

100°?

360° - 45° - 60° - 45° - 100° =110°

Angles around a point = 360°

PlenaryWhat are the missing

angles?

57°

a

46°

b89°

123°

45°

What are the missing angles?

150°X

YZ30°

150°

30°