1 Starter Questions Starter Questions A B C 5 12 27 o.

11

Starter QuestionsStarter Questions

1. Find the length the hypotenuse.

2. What is the name of the shape with this net.

3. Calculate the value of the missing angle.

A

B

C

5

12

27o

Learning IntentionLearning Intention

To investigate the special angle in a semi-circle.

Angles in a Semi CircleAngles in a Semi Circle

33

Tool-kit required

1. Protractor

2. Pencil

3. Ruler


44

1. Using your pencil trace roundthe protractor so that you have semi-circle.

2. Mark the centre of the semi-circle.

You should have something like this.


Mark three points

1. Outside the circle

x xx

x x

x x

x

x

2. On the circumference

3. Inside the circle


66

For each of the points

Form a triangle by drawing aline from each end of the diameter to the point.Measure the angle at the various points.

x

x

x

Log your results in a table. InsideCircumferenc

eOutside


77

InsideCircumferenceOutside

xx

x

< 90o

> 90o

= 90= 90oo

Online Demo


http://www.mathsrevision.com/index_files/angle_semi_circle.htm

KeyPoint for Angles in a Semi-circle

Angles in a Semi-CircleAngles in a Semi-Circle

A triangle ABC within a semicircle with base the length of the diameter

will ALWAYS be right angled at P on the circumference.

Remember - Angles in any triangle sum to 180o

B

A C

99

Hints

Example 1 : Sketch diagram and find all the missing angles.

70o

Look for right angle triangles43o

20o

47o

Remember ! Angles in any triangle

sum to 180o


Example 2 : Sketch the diagram.


C

A B

D

25o

60o

(a) Right down two right angle triangles

(a) Calculate all missing angles.

E

2 columns

Date

Exercise Number

Example of Good Work

Now try Ex 2Ch12 (page 138)Sketch shapes


1 Starter Questions Starter Questions A B C 5 12 27 o.

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