Q1 of 24 Page 227

I have made a closed right circular cone whose length of the base radius is 15cm and slant height is 24cm. Let us calculate the curved surface area and total surface area of that cone.

Base radius of the cone, r = 15 cm


Slant height of the cone, l = 24 cm


∴ Height of the cone, h = √(l2 – r2) = √(242 – 152) = √(576 – 225) = √351 = 18.73 cm


∴ Curved surface area of the cone,


= πrl cm2


= × 15 × 24 cm2


= 1131.43 cm2


∴ Total surface area,


= πr2 + πrl cm2


= 22/7 × 152 + 1131.43 cm2


= 707.14 + 1131.43 cm2


= 1838.57 cm2


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