11.2 Even and Odd Functions

11.2 Even and Odd Functions

• Even: $f(-x) = f(x)$ (graph symmetric about the $y$-axis). Example: $x^2$; also $\cos\theta$.
• Odd: $f(-x) = -f(x)$ (symmetric about the origin). Example: $x^3$; also $\sin\theta$.

$\cos(-\theta) = \cos\theta$ (even); $\sin(-\theta) = -\sin\theta$ (odd). For each $x$ in the domain, $-x$ must also be in the domain.