Transcript BASIC GEOMETRICAL IDEAS

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Geometry is the branch of mathematics which deals
with the properties and relations of line, angles,
surfaces and solids.
The word geometry is divided from two Greek words;
geo meaning ‘the earth’ and metron meaning ‘to
measure’. In ancient times, people needed to measure
earth or land so that they could bye or sell it. Just as
arithmetic deals with numbers, geometry deals with
figures, points and lines.
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A point is usually represented by a small dot
and is named by a single capital letter of he
alphabet.
A point has a position and we can ascertain its
location. However it has no magnitude i.e. it
has no length, breadth or thickness.
You can not draw an actual point on paper, no
matter how sharp a pencil you see.
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A line is straight and extends indefinitely on
both sides.
It has no end points and its length can not be
measured. Since a line extends indefinitely on
both sides you can not show a line on a paper
its totally. You can only show a part of it.
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A plane is a flat surface that extends indefinitely
in all directions.
Its dimensions can not e measured. Justas we can
not draw a a whole line on paper, we cannot a
whole plane either. We can only show a portion of
it. A table top, or the surface of walls of a room
are examples of portions of planes.
The figure shows two rays OA and OB starting
from the same initial point O. the figure that
they form is known angle. The common initial
point O is called the vertex of the angle. The
two rays OA and OB are called the arms of the
angle. An angle is formed by two rays starting
from the same initial point.
A triangle is a three-sided closed figure, formed
by three line segments. These three line segments
intersect in pairs. ABC is a triangle formed the
line segments AB , BC and CA. AB and BC
intersect in B. AC and BC intersect in C and AC
and AB intersect in A .
The length of the
perpendicular from the
vertical angle to the
base is called the
altitude of the triangle.
It is a measure of the
height of the triangle.
The line segments
joining the vertices to
the mid-points of the
opposite sides of a
triangle are known as
medians.
A quadrilateral is a four-sided figure . ‘Quadri’
means four, and ‘lateral’ means many sides.
HERE is a quadrilateral ABCD . It is formed
from the line segments AB, BC, CD and DA.
These line segments meet at their end points.
The quadrilateral ABCD has :
a) Four vertices A, B, C and D.
b) Four sides AB, BC, CD and DA.
ADJACENT SIDES :
Two sides of a quadrilateral which has a common
vertex are called its adjacent sides.
OPPOSITE SIDES :
Two sides of a quadrilateral which do not has a
common vertex, are called its opposite sides.
ADJACENT ANGLES :
Two angles of a quadrilateral which have a
common side are called its adjacent angles.
OPPOSITE ANGLES :
Two angles of a quadrilateral which do not have
a common side are called its opposite angles.
A circle is a set of points on a plane which are at
the same distance from a fixed point.
The fixed point O is called the centre of the circle
and the constant distance (OA, OB, OC, OD) is
known as the radius of the circle.