Question

4.
Find the curved surface area of a right circular cone whose slant height is 10 cm
and semi vertical angle is 30°.
(a) 120.8 sq cm
(b) 157.1 sq cm
(c) 170.3 sq cm
(d) 180 sq cm​

Answer 1

Answer:

Answer:

• Curved surface area of a right circular cone=157.1Sq cm

Given:

• Slant height,l=10cm
• Semi vertical angle=30°

To find:

• Curved surface area of a right circular cone.

Solution:

As we know that,

Semi vertical angle=30°

Slant height,l=10cm

In a right circular cone,

Base , length BC=Radius R

(Refer to the attachment)

Now, Cos 60°=l/R

1/2=10/R

R=5cm

So, Curved surface area of a right circular cone=πRl

CSA=3.14×5×10cm²

=3.14×50cm²

=157cm²≈157.1cm²

Hence, Curved surface area=157.1cm²

Step-by-step explanation:

Hope it helps you.....

Answer 2

$\bf{\underline{Question:-}}$

Find the curved surface area of a right circular cone whose slant height is 10 cm

and semi vertical angle is 30°.

(a) 120.8 sq cm

(b) 157.1 sq cm

(c) 170.3 sq cm

(d) 180 sq cm

$\bf{\underline{Solution:-}}$

By figure

In the right angle triangle ABC with 90° at B

And

∠A = 30° , ∠C = 60° { Because A+B+C = 180°}

So,

In this ∆

length BC = Radius of circular part of R.

i.e.,

→ R = L cos60° { cos 60° = 1/2 }

→ R = 10 cos 60°

→ R = 10 × 1/2

→ R = 5cm

______________________

So,

C.S.A of right circulation cone = πRl

C.S.A of right circulation cone = 22/7 × 5 × 10

C.S.A of right circulation cone = 1100 / 7

C.S.A of right circulation cone = 157.1 cm²

$\bf{\underline{Hence:-}}$

Curved surface area of right circular cone = 157.1 cm²

• Option ( b ) is right √√