Page 166 - Start Up Mathematics_4

Line

Extend the ray XY from the other end also. The figure that you X Y
get is a line.

Thus, a line segment extended on both sides is a line. It is written as XY or YX with
arrowheads on both sides. A line cannot be measured as it has no end points. It extends
indefinitely on both sides.
A line can be of many types.

Vertical Horizontal Slanting Curved lines
line line line
P Q
P P Q Q

Q P B
A

Angles B

arm
When two rays meet at a common end point, an angle is
formed. The common end point is called the vertex and the
two rays are called the arms of the angle. angle
A
To name an angle, the vertex is written in the middle and C
the points of the two arms are written on its either side. The vertex arm
symbol for an angle is ∠. In the given figure, the angle shown is written as ∠BAC or ∠CAB
and is read as angle BAC or angle CAB. AB and AC are the two arms of the angle.

Types of angles

Angles are mainly of four types

Right angle Acute angle Obtuse angle Straight angle
An angle formed by An angle less than An angle greater Two adjoining
a vertical line and a a right angle is an than a right angle is right angles form a
horizontal line is a acute angle. an obtuse angle. straight angle.
right angle.
D
E
A

B C B C F B C
B C ∠DBC is an acute ∠EBC is an obtuse ∠FBC is a straight
∠ABC is a right angle. angle. angle.
angle.

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