Find the area of metal sheet required in making a closed hollow cone of base radius 7 cm and height 24 cm.

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Solution

Base radius of cone (r)=7 cm and vertical height (h)=24 cm

$∴ S l a n t h e i g h t (l) = \sqrt{r^{2} + h^{2}} = \sqrt{(7)^{2} + (24)^{2}} = \sqrt{49 + 576} = \sqrt{625} = 25 c m T o t a l s u r f a c e a r e a = π r l + π r^{2} = π r (l + r) c m^{2} = \frac{22}{7} \times 7 (25 + 7) c m^{2} = 22 \times 32 c m^{2} = 704 c m^{2}$

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Find the area of metal sheet required in making a closed hollow cone of base radius 7 cm and height 24 cm.

Base radius of cone (r)=7 cm and vertical height (h)=24 cm ∴ Slant height (l)=√r2+h2=√(7)2+(24)2=√49+576=√625=25 cmTotal surface area=πrl+πr2=πr(l+r)cm2=227×7(25+7)cm2=22×32 cm2=704 cm2