A cone shape cup is made from a circular piece of paper of radius 7 by cutting out a sector and joining the edge AC and BC. Find the maximum (volume) of such a cup

Respuesta :

Answer:

The answer is "138.10"

Step-by-step explanation:

Let r also be cone base radius and h = the cone height.  

The radius for the original circle was on either side of the cone plied together = 7.  

The hypotenuse is 7, as well as a right triangle, is formed. So:

[tex]\to h^2+r^2 = 49\\\\ \to r^2 = 49-h^2[/tex]

Calculating the volume of the cone:

[tex]V = (\frac{1}{3}) \pi r^2 h \\\\[/tex]

   [tex]= (\frac{1}{3}) \pi (49 -h^2) h\\\\= (\frac{1}{3}) \pi 49h -h^3\\\\[/tex]

[tex]V'(h) = (\frac{1}{3}) \pi 49 - 3h^2\\\\[/tex]

Setting the derivative to zero and solving for h^2:

[tex]49-3h^2 = 0 \\\\ h^2 = \frac{49}{3} \\\\ r^2 = 49-\frac{49}{3} \\[/tex]

    [tex]= \frac{ 147 -49}{3} \\\\= \frac{98}{3} \\\\[/tex]

Calculating the maximum volume:

[tex]= \frac{1}{3} \pi \frac{98}{3} \frac{7\sqrt{3}}{3} \\\\= \frac{1}{3} \times 3.14 \times 32.66 \times 4.04 \\\\= \frac{1}{3} \times 3.14 \times 32.66 \times 4.04 \\\\= 138.10[/tex]