Question

In a triangle, two sides of 12 cm and 5 cm are at right angles. If the triangle is revolved along the 12cm side, the curved surface of the cone so formed will be (A) 156 cm2 (B) 78 cm2 (C) 65 cm2 (D) 130 cm2​

Answer 1

Step-by-step explanation:

this is the required solution.

options of this question are wrong

Answer 2

Mensuration- Cone

Given:

A right angled triangle having 12 cm and 5cm as sides.

Triangle is revolved around 12cm to form a cone.

To find:

Curved surface area of cone

Explanation:

I have attached the required figure for this question to understand.

Let the triangle given named as ΔABC with $AB= 12cm \ ,\ BC= 5cm$.

So according to Pythagoras  Theorem,

$AC^{2} =AB^{2} +BC^{2} \\AC^{2}= 12^{2} +5^{2}\\ AC^{2}=144+25\\AC^{2}=169\\AC=13$

We revolve ΔABC around side $AB(=12cm)$, to get a cone of height $12 cm$ and radius $5 cm$.

So, formula of curved surface area of cone is : $\pi rl$

where $l$ is the slant height of cone ( in this case it is 13cm)

So, CSA of cone ,

$\\\\\pi (5)(13)\\\\=\frac{22}{7}(5)(13)\\\\=204.1 cm^{2}$

Hence   $204cm^{2}$ is the Curved Surface Area.

Note: options are wrong .