L6 : Numericals - Practical Geometry , Maths, Class 8 Video Lecture - Class 8 | Best Video for Class 8

hello friends this video on practical
geometry part 6 is brought to you by
exam for calm no more fear from exam so
now that we have learned so many
different types of quadrilaterals it is
try a few draw a square read with re is
equal to five point one centimeter now
when it comes to a square what is the
speciality of a square in a square all
the four sides are exactly equal so
let's see if this is a square Reed and
if one side is five point one that means
that all the other sides are also equal
to five point one centimeters and in a
square all angles are equal to 90
degrees
now knowing all the angles and all the
sides it is very easy to draw the square
so let's draw any one side let's say we
draw our e then we draw angle R and
angle E is equal to 90 degree so let's
say this is our E and we have drawn and
then R is equal to 90 degree angle E is
equal to 90 degree and how you have to
draw a 90 degree for that when you would
need to draw first angle 60 then angle
120 using compass and then between angle
60 and angle 120 you would have 90 now
you draw an arc to mark point D because
the distance of D from point R would
also be five point one centimeter so
somewhere here let's say somewhere here
would be point D similarly some point
here would be point A and then you join
D and a so let's say if this is D if
this is a so what happens this distance
is also five point one because we
measure this distance and only then we
mark the points these are all five point
one and also you have drawn these 90
degrees so these are also 90 degrees
and that's how we get a square let's try
another one where we would draw a
rhombus whose diagonals are five point
two centimeters
and 6.4 centimeters long now in case of
a rhombus now we know certain properties
of rhombus the first property is that in
a rhombus the diagonals are
perpendicular to each other so in our
numbers diagonals are perpendicular so
that is one property of rhombus the
other property is that diagonals bisect
each other now we will see how we will
make use of these properties to draw the
wrong bus because to draw the rhombus we
would need to draw the sides also so
just knowing the two diagonals how will
we be able to draw this now let us say
this is just a rough sketch so let us
say this is a rhombus so for those
rhombus this is one diagonal and this is
another diagonal now what do we know we
know that the diagonals bisect each
other so basically let's say if this is
a rhombus a b c d when i say and they
intersect at a point
o when i say that the diagonals bisect
each other that would mean that a o is
equal to OC and b o is equal to OD and
when i say that the diagonals are
perpendicular that would mean that this
angle is always 90 degrees now let's see
that making use of these facts I'll be
able to draw the rhombus so for that
first of all we draw one diagonal so we
have chosen the diagonal AC which is
five point two centimeters so we have
drawn that now we draw an arc at the
midpoint
o now we are actually trying to find out
this point O so AC they have drawn so we
just need to draw an arc so put the
center of the capacitor draw an arc at
exactly the midpoint so what would be
the midpoint half of five point two
which would be two point six so at a
distance of two point six we would mark
the point O like here this is the point
O now these markings are
because you know I am just telling you
roughly where it would be so let's say
this is where the 0.0 is and now we draw
a perpendicular at O so we draw a line
perpendicular so we have drawn 90
degrees here 1.0 now we mark oh D is
equal to so now our job is to so we have
drawn a C we have drawn this
perpendicular also but we have to find
out where exactly this point B and this
point D lies so for that we know the
distance of OB and OD because the total
distance BD is given as 6 point 4
centimeters so if BD is 6 point 4 we
know that D o is equal to do so Bo and
do will be half of 6 point 4 which would
be 3 point 2 centimeters so from o we
mark the point D at a distance of 3
point 2 centimeters similarly we mark
the point B at a distance of 3 point 2
centimeters so now we have got all the 4
vertices of the rhombus that is ABC and
D so all we need to do is we need to
join a B BC C D and D in so that the
structure that we get is nothing but a
rhombus so you see just knowing the two
diagonals also we were able to draw a
rhombus that's because we knew the
properties of rhombus that the diagonals
are perpendicular and the diagonals
bisect each other so let us look at the
last problem where we are asked to draw
a rectangle with adjacent sides of
lengths 5 centimeter and 4 centimeter
now this is pretty simple because we
know let let us draw a rectangle so we
know that in a rectangle all these
angles are equal to 90 degrees so if we
say that ABCD is a rectangle if we know
a B has 5 centimeters and BC has 4
centimeters a in the opposite sides are
equal so this is also 5 this will go to
4 so knowing so much of detail it's
pretty simple to draw a rectangle so
first we draw any one side let's say a B
is equal to 5
centimeter is Tron then we draw
perpendicular from B again we draw
perpendicular from a now how we will
draw these perpendiculars I think I have
already discussed using compass you will
have to make an angle of 90 degrees at
these points so once you draw these
perpendiculars then you have to draw an
arc to mark BC is equal to 4 centimeters
so from point B keep the compass Center
here and then you make an arc at a
distance of four centimeters so wherever
you make that mark that is your Point C
similarly you make a mark by making an
arc at a distance of 4 centimeter from
point A so this point would be your
point D so now you join C D so what you
get ABCD is nothing but a rectangle so
with this we have reached towards the
end of this lesson and I hope that this
lesson on constructions would have
helped you now one important thing that
needs to be noted is the constructions
whichever I have done so far
like the quadrilaterals the
parallelograms or rectangles of the
squares now the measurements are not the
real measurements so I have just told
you the technique that you need to
follow to draw the construction so I
would advise you to try constructing the
same things again in your notebooks so
it is not necessary that many
quadrilaterals might not look the way it
is looking on the screen because on the
screen it is just a dummy diagram
because I am NOT measuring 5 centimeters
I am NOT measuring 4 centimeters so it
is just an approximate values ok
whatever let's say this point D is at a
distance of 4 centimeter so it is
something like that
so please draw them yourself just follow
the techniques with the help of these
examples which I have mentioned here and
I hope that that would help you so
whenever you start learning this lesson
on constructing quadrilaterals or
practical geometry I would advise you to
sit with your geometry box with a sheet
of paper so the during during the same
time when you are watching this video
also trying for low
also try to follow the instructions that
is being told in the video so that would
help you to actually understand this
session so with that I would like to
conclude this lesson so see you all in
the next lesson thank you please visit
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