Page 121 - Mathematics_Form_3

Circles

2. In the following figure, if E is the (c) d = 2 cm,
centre of the circle, answer the r = _____,
questions that follow. C = ______

A B ( d ) r = cm,
a __
FOR ONLINE READING ONLY
6
d = _____,
E C = ______

Central angles
D C Central angle in a circle is an angle
(a) Find the radius of the circle, formed by two radii that intersect at
given ‾ BD = 12 cm. the centre of the circle. The sides of a
(b) Find the diameter of the circle, central angle are radii that extend from
the centre and intersect the circle at two
given that ‾ CE = 6 cm. distinct Points, forming an arc between
3. Study the following circle with them. Engage in Activity 5.2 to enable
centre O, then identify the radius, you to identify a central angle of a circle.
diameter, and chord.
E
C Activity 5.2: Identifying the
central angle of a circle

Individually or in a group, perform the
Q O following tasks:
1. Use a pair of compasses to draw a
circle with centre O and radius of
Mathematics for Secondary Schools (a) r = 7 cm, 3. The two radii in task 2 form an
your choice.
D
R
2. From the centre, draw two radii
4. Given the radius r, diameter d
with end points P and Q on the
or circumference C of a circle,
circumference of the circle.
calculate the missing measures.
Round the answer to the nearest
angle at O. What is the name of
tenth (use π = 3.14).
the angle?
4. Use a protractor to measure the
d = _____,
angle and record the result.

C = ______
(b) C = 26 cm, 5. Using one of the radii as a reference
side, draw three more different
d = _____, angles and compare the magnitude

= ______ of each angle with its respective arc.

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