Cones

Formula > (pi*radius*height)+(pi*radius squared) = C.S.A + area base

Example One

Find the Total Surface Area of a cone, when given the radius of 7 and the height of 12.2

Method:

(pi*7*12.2)+(pi*7 squared)=422.230...

422(3 Sig.Fig)

Formula > pi*radius*slant height

Examples:

Find the C.S.A of a cone with radius of 4.2cm and slant height of 8.3cm. Give your answer to 3.S.F.

Method:

C.S.A = pi*r*l = pi*4.2*8.3

= 109.51...

=110cm

Formula > 1/3*pi*radius squared*perpendicular height

Examples:

Find the volume of a cone of radius 8cm and height 12cm. Give your answer to 3.S.F

Method:

(pi*8 squared*12) / 3 =804.247...

=804cm3

Formula > Volume of Large cone- Volume of Small cone.

Examples:

Find the volume of the frustrum of a cone made when a cone of radius 3cm and height 2cm is cut off the top of a cone of diameter 10cm and height 8cm (3SF) 

Method:

Large cone = (pi*5 squared*8) /3 = 209.439...

=209cm3

Small cone = (pi*3 squared*2)/3 = 18.849...

Volume of frustrum = 190.59... = 191 cm3