Question

f(x) = x4 - 50x2 + 3 (a) Find the intervals on which f is increasing. (Enter the interval that contains smaller numbers first.) ( , ) ∪ ( , ) Find the intervals on which f is decreasing. (Enter the interval that contains smaller numbers first.) ( , ) ∪ ( , ) (b) Find the local minimum and maximum values of f. (min) (max) (c) Find the inflection points. ( , ) (smaller x value) ( , ) (larger x value) Find the intervals on which f is concave up. (Enter the interval that contains smaller numbers first.) ( , ) ∪ ( , ) Find the interval on which f is concave down. ( ,

Answer 1

Answer:

  (-5, 0) ∪ (5, ∞)

Step-by-step explanation:

I find a graph convenient for this purpose. (See below)

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When you want to find where a function is increasing or decreasing, you want to look at the sign of the derivative. Here, the derivative is ...

  f'(x) = 4x^3 -100x = 4x(x^2 -25) = 4x(x +5)(x -5)

This has zeros at x=-5, x=0, and x=5. The sign of the derivative will be positive when 0 or 2 factors have negative signs. The signs change at the zeros. So, the intervals of f' having a positive sign are (-5, 0) and (5, ∞).