Q. Let f(x)=∣x∣1.Can we use the mean value theorem to say the equation f′(x)=−41 has a solution where 2<x<4 ?Choose 1 answer:(A) No, since the function is not differentiable on that interval.(B) No, since the average rate of change of f over the interval 2≤x≤4 isn't equal to −41.(C) Yes, both conditions for using the mean value theorem have been met.
Mean Value Theorem Conditions: The Mean Value Theorem states that if a function f is continuous on the closed interval [a,b] and differentiable on the open interval (a,b), then there exists at least one c in the interval (a,b) such that f′(c) is equal to the average rate of change of f over [a,b]. We need to check if f(x)=∣x∣1 meets these conditions on the interval [2,4].
Continuity Check: First, we check if f(x) is continuous on the closed interval [2,4]. Since ∣x∣ is never zero for x in [2,4], f(x)=∣x∣1 is continuous on [2,4].
Differentiability Check: Next, we need to check if f(x) is differentiable on the open interval (2,4). The function f(x)=∣x∣1 is not differentiable at x=0, but since 0 is not in the interval (2,4), we need to consider the differentiability elsewhere. The absolute value function ∣x∣ causes a problem at x=0, but since we are considering the interval (2,4), where x is always positive, we can write f(x) as (2,4)1 for this interval. The derivative of (2,4)1 is (2,4)3, which is defined for all x in (2,4).
Average Rate of Change Calculation: However, we must remember that the Mean Value Theorem requires the function to be differentiable on the entire open interval a,b. The function f(x)=∣x∣1 is not differentiable at x=0, and although x=0 is not in the interval 2,4, we must consider the behavior of the function at the endpoints to ensure there are no points of non-differentiability. Since ∣x∣ is not differentiable at x=0, and f(x) involves ∣x∣, we must conclude that f(x) is not differentiable at x=0. However, this does not affect the differentiability on the interval 2,4 since x=0 is not within this interval.
Conclusion: Now, we calculate the average rate of change of f(x) over the interval [2,4]. The average rate of change is given by b−af(b)−f(a), where a=2 and b=4. So, we have:f(4)=∣4∣1=41f(2)=∣2∣1=21The average rate of change is:4−241−21=2−41=−81
Conclusion: Now, we calculate the average rate of change of f(x) over the interval [2,4]. The average rate of change is given by b−af(b)−f(a), where a=2 and b=4. So, we have:f(4)=∣4∣1=41f(2)=∣2∣1=21The average rate of change is:4−241−21=2−41=−81The average rate of change of f over the interval [2,4] is [2,4]0, which is not equal to [2,4]1. Therefore, the Mean Value Theorem cannot guarantee that there is a number [2,4]2 in the interval [2,4]3 such that [2,4]4 because the average rate of change is not equal to [2,4]1.
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