Monday, September 10, 2012

Find the minimum of g(t)=t^3-25t+6 on the interval [-2.5, 5].

We have to find the minimum g(t)=t^3-25t+6 on the interval
[-2.5, 5].


First, we find the derivative of g(t). That is
equated to 0 to solve for x. The value of the second derivative is positive where the
function forms a
minimum.


g(t)=t^3-25t+6


g'(t)
= 3t^2 - 25


3t^2 - 25 =
0


=> t^2 =
25/3


=> t = -sqrt (25/3) and +sqrt
(25/3)


For these + sqrt(25/3) lies in the given
interval.


g''(t) for t = sqrt(25/3) is positive indicating
that we have a minimum.


The minimum value is [sqrt
(25/3)]^3 - 25*sqrt(25/3) + 6


=> (25/3)*(sqrt(25/3)
- 25*sqrt(25/3) + 6


=> sqrt(25/3)[25/3 - 25] +
6


=> (-50/3)*sqrt(25/3) +
6


=> -250/3*sqrt 3 +
6


The required minimum of g(t)= t^3-25t+6 on
the interval [-2.5, 5] is -250/(3*sqrt 3) + 6

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