2021 · Q74
ABC is a triangle right-angled at B with AB = 8 cm and BC = 6 cm. It is made to revolve about its side BC. What is the approximate total surface area of the cone so formed ? (take π = 22/7)
Elementary MathematicsMensuration
- A452 cm²
- B440 cm²
- C432 cm²
- D420 cm²
Explanation
Revolving about BC gives a cone with radius r = AB = 8 cm, height h = BC = 6 cm, and slant height l = √(8²+6²) = 10 cm. Total surface area = πr(l + r) = (22/7)·8·18 = 3168/7 ≈ 452.6 cm². The nearest option is (a) 452 cm².