Question

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The radius of a cone is 7 cm . It's veritical angle is 60°. It's curved surface area is kπ square cm . Find the value of k .
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Answer 1

Answer: k = 98 cm

Step-by-step explanation: By doing construction , draw the height of the cone.

the vertical angle is divided into two parts i.e. 30°

by applying trigonometry in the formed triangle with ∅=30°

∴ tan∅=P/B

let us take the radius as perpendicular and height as base

( as ∅ lies between base and hypotenuse and here 30° is the ∅ )

tan 30°= 7/height

1/√3=7/height

by cross multiplication

height of the cone = 7√3 cm

Curved surface area of cone = πrl

l= slant height = √(height)²+(radius)²=√(7√3)²+(7)²=√147+49=√196=14 cm

C.S.A. of cone =πrl

πrl = πk ( C.S.A. OF CONE =πk)

rl = k (∵as the value of π is same on LHS and RHS)

7×14 = k

k= 98 cm

               

Answer 2

$\bf\huge{Question:-}$

The radius of a cone is 7 cm . It's veritical angle is 60°. It's curved surface area is kπ square cm . Find the value of k .

$\bf\huge{answer:-}$

k=98cm