Question

the radius and slant height of a cone are in the ratio 4:7. If it's covered surface area is 792cmsquare. Find it radius

Answer 1

Given,

radius:slant height=4:7

Curved Surface Area of cone=792cm2

Let the radius of cone be 4x and slant height be 7x

Now, According to question,

Curved Surface Area= pi*r*l

=>792=22/7*4x*7x

=> 792*7/22=28x2

=> 36*7/28 =x2

=> 4*9*7/7*4= x2

=> 9=x2

=> plus/minus3=x

Since radius cannot be negative,

=>x=3

Therefore The required answer,

Radius= 4*x=4*3=12 cm

Hope it helps!!!

Answer 2

radius and slant height in ratio= 4:7
so we assume 4a:7a

so radius = 4a
height = 7a
coverred surface area =curved surface area (22/7*r*l)= 792sqcm.

792cmsq=22/7*4a*7a
a^2 = 792/22*4 = 792/88 = 9

a=3cm.

radius = 4a =4*3=12cm....



hope this helps...................