Examples: Surface area of Cone Video Lecture - Class 9

hello friends this video on surface area
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there's a few more questions to
understand it wasn't a corn cob shaped
somewhat like a cone has a radius of its
protest and past two point one
centimeter so this is almost take the
corner this is this one in the length
the same plane
they have nation it is height it is not
they didn't hide this is the length that
is 20 and if each one centimeter square
of the surface of the cob carries an
average of four grains how many grains
could you find on the into I college so
that means we have to first find the
curve surface area right so in this area
this in here there is no con you know
that we this is something we know
because we eat corn that is implicit
spear to first find a curved surface of
the cone or you can say kotts it is PI R
M okay so but L is not even H is so L
will be at the first night L is regard
square plus X square we know this put
the values R square is 2.1 square H
square H is what would be okay anyway so
you saw all there is you get almost
twenty in this twenty point one one that
is the value of L so let's find the
si this pi RL there is 22
by 7 into R that is 2.1 L that is 2014 1
1 so let me say it a meter square you
saw this you get one thirty two point
seven two
is centimeter square okay so one
centimeter square of call has has food
raised so one thirty two point seven to
six centimeter square call will have
hominy four into one thirty two point
seventy through six grains so we saw
this wait five thirty point nine two and
that is almost 531 grades so that is the
number of grains this particular corn
cob okay it's pretty easy so this was it
is mentioned that it looks like one key
word here is corn
so the key word in his cone and the
lemon the height of the cone was given
the radius of the cone was given and it
was mentioned that English averaged one
centimeter square surface in the or the
cone will have four grains and with that
we could actually find the number of
players in the whole concoct the curve
surface area of the cone is given three
zero eight centimeter square slant
height is 14 centimeter you define the
radius of the base and the total surface
area of the wound
so it's pretty easy straightforward
question way we know that caress a is
something but fire put the value 3 0 8
centimeter square that's five minutes to
play seven into are all of you to find
slant height L is given so you saw all
this and this is 14 centimeter so you
saw there's you get RS 7 centimeter one
part of salt pretty easy
second is total surface area total that
means me is what for Khun total surface
area or Cole is water let's say plus PI
R square correct so if you notice in the
case of cylinder the total surface area
of a skirt surface area plus 2 pi X but
they were two V's in cone there's only
one base so PI R square now does it 3-0
8 plus pi is 2 8 by 7 RBIs formed 7 2 7
centimeter squared so you saw this
becomes 3 through 8 this becomes 1 54
centimeter square and then it's 462
ok let's take another question a conical
tent 10 meter eyes with 10 meter radius
of the base is given 24 meter find the
slime type slightly this PTZ L is equal
to root r square plus X but what is the
value of R is 24h 10 and this is nothing
but root 676 by 76 because sunlight 676
that is 26 meter this is by 7676
so 676 maple is nothing but 26 meter
that is a slant height first person
system cost of canvas required to make
the tank at the cost of one meter square
so here we have to find what we have to
find such a city because in the tent
actually one thing is not clear in this
case it does not mention that we do
believe the base also right so tell Azul
base is not required because else they
would have given that the base has to be
created right so we'll just assume that
curved surface area has to be creative
so curved surface any of the cone we
know is nothing but PI R value 22 by 7 R
this one is 24 L is 126 and that will be
meter square okay so that is the curves
of this area
what if the costs will not multiply now
because it has to divide place seventh
we don't have the number so we'll just
keep his number asses Hey so cost of one
meter square is what 70 rupees so cost
of these many meter square is 1 2 by 7
into 24 to 26 meter square is what you
see you number into 70 and there will be
rubies so in this case it gets canceled
so you saw this you get 1 2 3 7 to 8
slow it easy this was confusing because
in this case they have not mentioned
either the base has to be created or not
so we assume that the base is not
required
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