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Question Number 25744 by rita1608 last updated on 13/Dec/17

find the surface area of the solid   formed by the rotation of the arc of   the cycloid x=a(t+sin t),   y=a(1+cost) about x axis

findthesurfaceareaofthesolidformedbytherotationofthearcofthecycloidx=a(t+sint),y=a(1+cost)aboutxaxis

Answered by ajfour last updated on 14/Dec/17

(dx/dt)=y      (dy/dx)=((−sin t)/((1+cos t)))  (√(1+((dy/dx))^2 )) =(√(1+((sin^2 t)/((1+cos t)^2 ))))          =((√2)/(1+cos t))  S=2∫_0 ^(  π) (2πy)(√(1+((dy/dx))^2 ))dx     =4π∫_0 ^(  π) [a(1+cos t)]^2 [((√2)/(1+cos t))]dt    =4(√2)πa^2 ∫_0 ^(  π) (1+cos t)dt    =4(√2)π^2 a^2  .

dxdt=ydydx=sint(1+cost)1+(dydx)2=1+sin2t(1+cost)2=21+costS=20π(2πy)1+(dydx)2dx=4π0π[a(1+cost)]2[21+cost]dt=42πa20π(1+cost)dt=42π2a2.

Commented by rita1608 last updated on 14/Dec/17

why 2 is multiplied , in some   questions 2 is not multiplied plss tell  me when 2 is multiplied

why2ismultiplied,insomequestions2isnotmultipliedplsstellmewhen2ismultiplied

Commented by ajfour last updated on 15/Dec/17

if there exists a line/plane of  symmetrtry we can find only  half the length/surface area/  volume and double it.

ifthereexistsaline/planeofsymmetrtrywecanfindonlyhalfthelength/surfacearea/volumeanddoubleit.

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