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CBSE Class 9 Answered

An isosceles triangle with a base radius of 0.4 m and an altitude of 0.3 m is revolved about a line through the vertex and perpendicular to the base. Calculate the lateral surface area of the solid so generated.
Asked by Topperlearning User | 17 Oct, 2017, 08:23: AM
answered-by-expert Expert Answer

The solid generated by revolving the triangle is a cone with height (h) = 0.3 m and radius (r) = 0.4 m

begin mathsize 12px style straight l squared equals straight r squared space plus space straight h squared straight l space equals square root of space straight r squared space plus space straight h squared end root straight l space equals space square root of 0.4 squared plus 0.3 squared end root straight l space equals space 0.5 space straight m end style

Thus, l = 0.5 m

begin mathsize 12px style Curved space surface space area space equals space πrl space equals 22 over 7 cross times 0.4 cross times 0.5 equals fraction numerator 4.4 over denominator 7 end fraction equals 0.63 space straight m to the power of 2 space space end exponent left parenthesis approx. right parenthesis end style

Answered by | 17 Oct, 2017, 10:23: AM

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