Finding intervals of increase/decrease and classifying the critical point
Consider the function defined on the closed interval .
The derivative of is . This derivative has exactly one zero on , located at approximately (you do not need to solve for this value exactly — you may take it as given). Using the first derivative test, determine the intervals on where is increasing and where it is decreasing, and state whether has a local maximum or a local minimum at this critical point.
Hint
Pick a test value on each side of (for instance and ) and check the sign of there. Use those signs to determine where is increasing/decreasing and to classify the critical point.
Step-by-step solution
First, test a point to the left of , say : , so is increasing on . Next, test a point to the right, say : . Wait—this suggests is positive on both sides. Let me recalculate more carefully.
Testing more carefully with (just left of ): . Testing (just right of ): . Hmm, both are still positive. Let me test to the left: . It appears that throughout .
Since for all , the function is increasing on the entire interval . The point where is an inflection point or a point where the derivative momentarily touches zero but does not change sign. Therefore, has neither a local maximum nor a local minimum at .
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