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Questions  

If  θ is the angle (semi-vertical) of a cone of maximum volume and given  slant height, then  tan θ is given by

a
2
b
1
c
2
d
3

detailed solution

Correct option is C

Let OB=1,OA=1cos⁡θ and AB=1sin⁡θ(0≤θ≤π/2). Then  V=π3(AB)2(OA)=π3l3sin2⁡θcos⁡θ⇒ dVdθ=π3l3sin⁡θ3cos2⁡θ−1 So from dV/dθ=0, we get θ=0 or cos⁡θ=1/3.  Also, V(0)=0,V(π/2)=0 and Vcos−1⁡13=2πl393 Hence V is maximum when cos⁡θ=1/3, i.e. tan⁡θ=2

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