The volume of a frustum of a right circular cone is 52π cm*. Its altitude is
3cm and the measure of its lower radius is three times the measure of its
upper radius.
1. What is the radius of the upper base?
2. What is the slant height of the frustum?
1
Expert's answer
2020-11-19T18:14:27-0500
Joining a smaller cicular cone on the top,we have a complete triangler1h1=r2h1+h2By the law of similar trainglesh1is the height of the smaller coneh2is the height of the larger coner2=3r1r1h1=3r1h1+h2r1h1=3r1h1+3h1=3h1+33h1=h1+32h1=3,h1=23V=π(r22(23+3)−r12×23)=52π=π(9r12(23+3)−r12×23)=52π9r12(23+3)−r12×23=529r12⋅29−r12×23=52281r12−23r12=52278r12=52278r12=5239r12=52r12=34r1=32∴The upper radius is32cmSlant height of the larger cone is=r22+(h1+h2)2Slant height of the smaller cone is=r12+h12Slant height of the larger cone is=(3×32)2+(29)2=12+(29)2=12+481=448+81=4129=2129Slant height of the smaller cone is=34+(23)2=34+49=1216+27=1243=2343∴The slant height of the frustum is=2129−2343=2129−6129=3129∴The slant height of the frustum is3129cm
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