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Maximization & Minimization

Maximum and minimum values of a function can be found, like in a cartesian plane. The methods and finding, as well as that of testing the nature of the point, are the same.

A solid right cylinder is removed from a solid sphere of radius 10cm, as shown. If the height of the cylinder is 4x cm, show that the volume of the cylinder is V = 400px - 16px3. Find the maximum volume of the cylinder as x varies.
 
Solution:
 
Diameter of the cylinder, by Pythagoras Theorem
             
Radius of cylinder
             
 
Volume
              shown
 
dV/dx = 400p - 48px2
 
At stationary point, dv/dx = 0
              400p = 48px
                  x2 = 25/3
                                 reject negative answer as x > 0
 
              d2V/dx2 = -48px
 
        when ,
              d2V/dx2 < 0    ----> maximum point
 
Volume