Explanations & Calculations
- Lateral surface area of a cone is given by A=πrL
- Therefore, by careful inspection, the needed area is
A1=πR(L+x)−πrx=π[RL+x(R−r)]⋯(1) Rr=Base face radius=upper face radius of the fusrtum
- Considering the equiangular triangles ABE & ACD,
105h=12+hh=12cm
- By Pythagoras theorem to ABE triangle,
x2x=122+52=13cm
- Considering the equiangular triangles ACD & ABE,
510L=xL+x=13cm
A1=π[10×13+13×(10−5)]=612.61cm2
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