Given the function # f(x) = 9/x^3#, how do you determine whether f satisfies the hypotheses of the Mean Value Theorem on the interval [1,3] and find the c?

Answer 1
You determine whether it satisfies the hypotheses by determining whether #f(x) = 9/x^3# is continuous on the interval #[1,3]# and differentiable on the interval #(1,3)#.
You find the #c# mentioned in the conclusion of the theorem by solving #f'(x) = (f(3)-f(1))/(3-1)# on the interval #(1,3)#.
#f# is continuous on its domain, which includes #[1,3]#
#f'(x) = (-27)/x^4# which exists for all #x != 0# so it exists for all #x# in #(1,3)#

Therefore this function satisfies the hypotheses of the Mean Value Theorem on this interval.

To find #c# solve the equation #f'(x) = (f(3)-f(1))/(3-1)#. Discard any solutions outside #(1,3)#.
I believe that you should get #c = root(4)(54/13)#.
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Answer 2

To determine if f(x)=9x3 f(x) = \frac{9}{x^3} satisfies the hypotheses of the Mean Value Theorem on the interval [1,3][1, 3], we need to verify if the function is continuous on the interval [1,3][1, 3] and differentiable on the interval (1,3)(1, 3).

  1. Continuity: f(x)=9x3 f(x) = \frac{9}{x^3} is continuous on the interval [1,3][1, 3] because it is a rational function, and the denominator x3 x^3 does not equal zero on this interval.

  2. Differentiability: f(x)=9x3 f(x) = \frac{9}{x^3} is differentiable on the interval (1,3)(1, 3) because it is a composition of continuous functions, and its derivative f(x)=27x4 f'(x) = -\frac{27}{x^4} is defined and continuous on (1,3)(1, 3) except at x=0 x = 0 .

Since f(x)=9x3 f(x) = \frac{9}{x^3} satisfies both conditions, it satisfies the hypotheses of the Mean Value Theorem on the interval [1,3][1, 3].

To find the value c c guaranteed by the Mean Value Theorem, we use the formula:

f(c)=f(3)f(1)31f'(c) = \frac{f(3) - f(1)}{3 - 1}

First, find f(3) f(3) and f(1) f(1) :

f(3)=933=927=13f(3) = \frac{9}{3^3} = \frac{9}{27} = \frac{1}{3} f(1)=913=9f(1) = \frac{9}{1^3} = 9

Now, find f(c) f'(c) by finding the derivative of f(x) f(x) and solving for c c :

f(x)=27x4f'(x) = -\frac{27}{x^4}

f(c)=27c4f'(c) = -\frac{27}{c^4}

Now, set f(c) f'(c) equal to the average rate of change:

27c4=13931=1392=26232=263-\frac{27}{c^4} = \frac{\frac{1}{3} - 9}{3 - 1} = \frac{\frac{1}{3} - 9}{2} = \frac{-26\frac{2}{3}}{2} = -\frac{26}{3}

Solve for c c :

27c4=263-\frac{27}{c^4} = -\frac{26}{3} c4=2726c^4 = \frac{27}{26} c=27264c = \sqrt[4]{\frac{27}{26}}

So, the value of c c guaranteed by the Mean Value Theorem lies in the interval (1,3) (1, 3) and is approximately 27264 \sqrt[4]{\frac{27}{26}} .

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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