Page 157 - ICSE Math 6

Perpendicular lines l

Two intersecting lines are said to be perpendicular if they meet at an angle of
90°. In the adjoining figure, line l is perpendicular to line m and is represented
by l ⊥ m (read as l is perpendicular to m). 90° m

Perpendicular bisector
A line which cuts a given line segment into two equal parts at 90° is called l
perpendicular bisector of the given line segment.
In the given figure, line l is the perpendicular bisector of the line segment CD, 90°
and point O lies exactly between the points C and D. C O D

Open and Closed Figures

The figures which have different beginning and end points are known as open figures and the figures
which have the same beginning and end points are known as closed figures.

Open figures Closed figures

Triangle

A triangle is a closed figure formed by three line segments which are joined at A
their end points. A triangle ABC is written as DABC. The line segments AB, BC
and CA are known as the sides of the triangle. The point at which any two sides
meet is known as the vertex of the triangle. So, there are three vertices in DABC
namely, A, B and C. Also there are three angles, angle A, angle B and angle C.
B C
Rectangle
A rectangle is a closed figure formed by four line segments (sides) such that D C
the opposite sides are equal and each angle is of 90°. So, in a rectangle ABCD,

AB = DC, AD = BC, and
angle A = angle B = angle C = angle D = 90° A B

Square D C
A square is a closed figure formed by four line segments (sides) such that all the
four sides are equal and each angle is of 90°. So, in a square ABCD,
AB = BC = CD = DA, and

angle A = angle B = angle C = angle D = 90° A B

Circle
A circle is a closed figure. A circle is a set of points in a plane whose distance A
from a fixed point remain constant. The fixed point is known as the centre of O
the circle and the distance of any point on the circle from the centre is known
as the radius of circle. In the adjoining figure, O is the centre of the circle and C
OA = OB = OC = radius of the circle. B

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