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An angle is denoted using the symbol ‘∠’ and capital letters at the vertex and at the ends
of the two arms of the angle. For instance,
P
Thus, ∠PQR = 40° or ∠RQP = 40°
^ ^
or PQR = 40° or RQP = 40°
40°
Q R or ∠Q = 40°

Self Practice 8.1a

1. Explain whether line segments PQ and RS in each of the following diagrams are
congruent:
(a) (b) R (c)
3 cm Q P 4.2 cm
P
R 3.3 cm Q 3.2 cm Q
3 cm 4.2 cm S
P
S R
S

2. Explain whether ∠PQR and ∠ABC in each of the following diagrams are congruent:
(a) P B (b) P (c) R
R 138° R A
A Q
32° Q B 256° CHAPTER
32° B P 256°
136°
Q A C C C 8

How do you estimate and measure the length LEARNING
of a line segment and the size of an angle? STANDARDS
Estimate and measure
The length of a line segment can be estimated by comparing the size of line segments
the length with objects of a known length. For instance, if an and angles, and explain
eraser is known to have a length of 4 cm, then the length of how the estimation
line AB below can be estimated as approximately 10 cm. is obtained.
A B

ERASER ERASER ERASER

4 cm 4 cm 2 cm

The length of a line segment can be measured more accurately by using a ruler.
P Q

The length of line segment
PQ is exactly 6 cm. 0 cm 1 2 3 4 5 6

171
Lines and Angles

08 TB Math F1.indd 171 11/10/16 12:17 PM