Question

Area of the base of a cone is 1386 sq.cm.and it's height is 28cm. .Find it's surface area.

Answer 1

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=) In the example

Given :

Area of the base of a cone = 1386sq.cm.

Height,h= 28cm.

Surface are = ??

Therefore by using the formula ,

Area of base of cone = pi*r^2

1386 = 22/7*r^2

1386*7/22 = r^2

63*7 = r^2

441 = r^2

r = 21cm.

We got the radius.

Now we find the slant height,

We know that,

l^2 = r^2 + h^2

l^2= (21)^2 + (28)^2

l^2 = 441 + 784

l^2 = 1225

l = 35cm.

So we got the value of radius and slant height now we can easily find the surface area of cone.

By using the formula,

Surface are of a cone= pi * r*l

= 22/7*21*35

=22*3*5

= 330sq.cm.

I hope this will helps you.

Thanks.

Answer 2

Answer:

Step-by-step explanation:

Area of the base of a cone = 1386sq.cm.

Height,h= 28cm.

Surface are = ??

Therefore by using the formula ,

Area of base of cone = pi*r^2

1386 = 22/7*r^2

1386*7/22 = r^2

63*7 = r^2

441 = r^2

r = 21cm.

We got the radius.

Now we find the slant height,

We know that,

l^2 = r^2 + h^2

l^2= (21)^2 + (28)^2

l^2 = 441 + 784

l^2 = 1225

l = 35cm.

So we got the value of radius and slant height now we can easily find the surface area of cone.

By using the formula,

Surface are of a cone= pi * r*l

= 22/7*21*35

=22*3*5

= 330sq.cm.

I hope this will helps you.

Thanks.