Answer to Question #187581 in Geometry for John

Question #187581

a large cone has a height 6 cm and base diameter 18 cm. The large cone is made by placing a small cone of height 2 cm and base diameter 6 cm on top of a frustum B.


Calculate the volume of the frustum B. Give your answer in terms of π.​​​​​​​​

 

Calculate the total surface area of frustum B. Give your answer in terms of π.


1
Expert's answer
2021-05-07T12:31:22-0400

Volume of frustum of cone=πh(r12+r22+r1r2)3Volume \ of\ frustum\ of\ cone=\dfrac{{\pi}h(r_1^{2}+r_2^{2}+r_1r_2)}{3}

r1=9 cmr_1=9\ cm

r2=3 cmr_2=3\ cm

 h=2 cm\ h=2\ cm

where r1,r2 radiuswhere\ r_1,r_2 \ radius of frustum and h1 height offrustum.\ of\ frustum\ and\ h_1\ height\ of frustum.

Now putting all the value in above formula, we get

V=πh(r12+r22+r1+r2)3=π×2(92+32+9×3)3=78π cm3V=\dfrac{{\pi}h(r_1^{2}+r_2^{2}+r_1+r_2)}{3}=\dfrac{{\pi}\times 2( 9^{2}+ 3^{2}+9\times3)}{3}=78{\pi}\ cm^{3}


Total surface area offrustum=π(r12+r22+(r1+r2)×(r1r2)2+h2)=Total\ surface \ area \ of frustum={\pi}({r_1^{2}}+{r_2^{2}}+(r_1+r_2)\times \sqrt({{r_1-r_2})^{2}+h^{2}})=π×(92+32+9+3+(93)2+22){\pi}\times(9^{2}+3^{2}+9+3 +\sqrt {(9-3)^{2}+2^{2}})=216.64 π{\pi}


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