Page 165 - ICSE Math 7

Collinear Points A

Three or more points are known as collinear points if all C
of them lie on the same line, otherwise they are known as P Q
non-collinear points. R B
Collinear points Non-collinear points
Concurrent Lines

Three or more lines are known as concurrent lines if all of p q l m
them pass through the same point, otherwise they are known r n
as non-concurrent lines. The common point of intersection A
of concurrent lines is known as the point of concurrence.
In the adjoining figure, p, q and r are concurrent and A is Concurrent lines Non-concurrent lines
the point of concurrence.

Angle

Two rays having the same initial point form an angle. In the adjoining P
figure, two rays QP and QR having the same initial point Q form ∠PQR
(read as angle PQR). Rays QP and QR are called the sides or arms of sides
∠PQR and their common initial point Q is known as the vertex. An
angle can also be named by its vertex, such as ∠Q or by numbers or Q R
small letters such as ∠1, ∠2, etc. or ∠a, ∠b, etc. vertex
Measurement of an angle
The turn that one arm of an angle takes to reach the other arm is its magnitude.
The unit for measuring an angle is degree denoted by ‘°’. The angle made by

a ray, say PQ while completing a rotation around the vertex P is 360°. When P Q
we divide 360° into 360 equal parts, then each part is 1°. If we further divide 1° into 60 equal parts,
then each part is known as a minute denoted by a single prime ‘′’. If 1′ (read as 1 minute) is again
divided into 60 equal parts, then each part is known as a second denoted by two primes ‘″’. So,
1 complete rotation = 360° (three hundred sixty degrees)
1° = 60′ (sixty minutes) Maths Info
1′ = 60″ (sixty seconds) Sum of angles around a point
is always 360°.
Types of angles
On the basis of their magnitudes, angles are divided into the following
categories.

Acute angle P

An angle whose magnitude is more than 0° but less than 90° is called
an acute angle. For example, angles with magnitude 25°, 38° or 88° are
acute angles. Q R

Right angle P
An angle whose magnitude is 90° is called a right angle.
90°
Q
R

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