5.3 The second derivative test
www.whitman.edu › mathematics › calculus_onlineMay 03, 2018 · Sometimes the test fails, and sometimes the second derivative is quite difficult to evaluate; in such cases we must fall back on one of the previous tests. Example 5.3.2 Let f ( x) = x 4. The derivatives are f ′ ( x) = 4 x 3 and f ″ ( x) = 12 x 2. Zero is the only critical value, but f ″ ( 0) = 0, so the second derivative test tells us nothing.