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find the dimensions (radius r and height h) of the cone of maximum volume that can be inscribed in a sphere of radius 2.

Sagot :

The dimensions of the radius is 4/3[tex]\sqrt{2}[/tex] and that of height is 8/3.

Let r be the radius of the cone,  be the radius of the sphere and h be the height of the cone.

Let's put DˆOB=x with limitations 0≤x≤π.

In the right-angled triangle DOB:

r=DB=Rsinx, OD=Rcosx, than

h=CD=OC+OD=R+Rcosx=R(1+cosx).

So the volume of the cone is:

V=1/3πr²h ⇒V=1/3π(Rsinx)²⋅R(1+cosx)

V=1/3πR³sin²x(1+cosx)

V'=1/3πR³⋅[2sinx⋅cosx⋅(1+cosx)+sin2x(−sinx)]

  =1/3πR³sinx[2cosx(1+cosx)−sin2x]

  =1/3πR³sinx(2cosx+2cos2x−sin2x)

  =1/3πR³sinx(2cosx+2cos2x−1+cos2x)

 =1/3πR³sinx(3cos2x+2cosx−1)

Now let's find the signum of the derivative, since sinx≥0 for every x in the limitations, then:

V'≥0⇒3cos²x+2cosx−1≥0

      ⇒Δ/4=(b/2)²−ac =1+3=4

cosx=(−b/2)±√Δ/4 / a

      =−1±2/3,

So:

cosx≤−1∨cosx≥1/3

The first one has only the solution:

x=π

the second:

−arccos(1/3)≤x≤arccos(1/3), but for the limitations:

0≤x≤arccos(1/3).

The function gros from zero to arccos(1/3), and then it decreases.

So x=arccos(1/3) is the maximum requested.

Let's find now r and h:

r=Rsinx

 =R√1−cos2x

 = 2√1−(1/3)²

 = 2√1−1/9

 =2√9−1/9

 =2√8/9

 =2⋅2√2/3

 =4/3√2

h=R(1+cosx)=2(1+1/3)

 =2(3+1/3)

=8/3.

Therefore the radius is 4/3√2 and the height is 8/3.

To know more about the cone refer to the link given below:

https://brainly.com/question/1082469

#SPJ4

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