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Critical points of sin(pi·x)

\sin{\left(\pi x \right)}

Step by step

  1. f(x) = \sin{\left(\pi x \right)}

    Critical points are where f′(x) = 0 or is undefined.

  2. f'(x) = \pi \cos{\left(\pi x \right)}

    Differentiate.

  3. x = \frac{1}{2}, x = \frac{3}{2}

    Solve f′(x) = 0.

  4. f''(x) = - \pi^{2} \sin{\left(\pi x \right)}

    Second-derivative test: f″ < 0 → maximum, f″ > 0 → minimum.

  5. f''(\frac{1}{2}) = - \pi^{2} \Rightarrow (\frac{1}{2}, 1) \text{ is a local maximum}

  6. f''(\frac{3}{2}) = \pi^{2} \Rightarrow (\frac{3}{2}, -1) \text{ is a local minimum}

Reveal the answer
(\frac{1}{2}, 1)\ \text{local maximum},\; (\frac{3}{2}, -1)\ \text{local minimum}