Find the local maximum and minimum of $LaTeX: \displaystyle f(x) = - 7 x^{3} + 26 x^{2} - 7 x + 2$ .

To find the critical numbers solve $LaTeX: \displaystyle f'(x) = 0$ . The derivative is $LaTeX: \displaystyle f'(x) = - 21 x^{2} + 52 x - 7$ . Solving $LaTeX: \displaystyle - 21 x^{2} + 52 x - 7 = 0$ gives $LaTeX: \displaystyle x = \left[ \frac{1}{7}, \ \frac{7}{3}\right]$ . Using the 2nd derivative test gives:
$LaTeX: \displaystyle f''\left( \frac{1}{7} \right) = 46$ which is greater than zero, so the function is concave up and $LaTeX: \displaystyle f\left(\frac{1}{7}\right) = \frac{74}{49}$ is a local minimum.
$LaTeX: \displaystyle f''\left( \frac{7}{3} \right) = -46$ which is less than zero, so the function is concave down and $LaTeX: \displaystyle f\left(\frac{7}{3}\right) = \frac{1034}{27}$ is a local maximum.