Q2 of 35 Page 201

What is the surface area of a cone of base diameter 30 centimetres and height 40 centimetres?

height of the cone = 40 cm

Base diameter = 30cm


Base radius


l = slant height


Applying Pythagoras theorem, we get:


l = √(h2 + rb2)


= √(402 + 152)


= √(1600 + 225) = √1825 cm


We know that, Curved surface area of cone = πrbl


Where rb = base radius and l = slant height


Curved surface area of cone = π× 15× √18255 = 640.8π cm2


Surface area of base = πrb2 = π × 152 = 225π cm2.


Total surface area = (640.8 + 225)π = 865.8π cm2


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