Ex. (4) Area of the base of a cone is 1386 sq.cm and its height is 28

1.	Ex. (4) Area of the base of a cone is 1386 sq.cm and its height is 28 cmFind its surface area. (Ď =-)
Answer» Area of the base of a cone = 1386sq.cm. Height,h= 28cm. Surface are = ?? Therefore by using the formula , Area of base of cone = pir^2 1386 = 22/7r^2 13867/22 = r^2 637 = 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 * rl = 22/72135 =223*5 = 330sq.cm.

Ex. (4) Area of the base of a cone is 1386 sq.cm and its height is 28 cmFind its surface area. (Ď =-)

Answer»

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.