Question

the radius of a cone is 3cm and vertical height is 4cm.find the area of the curved surface
[ans. 62.85 cm^2]
solve and find the answer given below​

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Answer 1

Curved surface area of a cone = πrl

where l = √ (r2 + h2 )

Given r = 4 cm and h = 3 cm

l = √ (42 + 32 ) = 5 cm

Curved surface area of a cone = (22/ 7) x 4 x 5

= 62.85 cm2 .

Answer 2

Given :-

• Radius = 3 cm
• Height = 4 cm

To Find :-

CSA

Solution :-

At first we know that

CSA = πrl

But,

Slanght height isn't given. So, by using Pythagoras theorem.

Pythagoras theorem :- In this theorem a mathematician Pythagorean, discovered a new formula called Pythagoras theorem. In it the sum of squares of base and height is same as the square of Hypotenuse.

Here,

Hypotenuse = l

Base = r

Height = h

So,

By putting values

$\large \sf \: { \ell}^{2} = {3}^{2} + {4}^{2}$

$\sf \implies \ell {}^{2} = 9 + 16$

$\sf \implies { \ell}^{2} = 25$

$\sf \implies { \ell}= \sqrt{25}$

${ \frak {\red {\underline{ \ell \: = 5}}}}$

Now,

CSA = 22/7 × 3 × 5

CSA = 22/7 × 15

CSA = 47.1 cm²