Even Odd
1. Problem: For each function, find $f(-x)$ and $-f(-x)$, then compare with $f(x)$ to determine if the function is even, odd, or neither.
2. Function a) $f(x) = x^2 - 4$
- Compute $f(-x) = (-x)^2 - 4 = x^2 - 4$
- Compute $-f(-x) = -(x^2 - 4) = -x^2 + 4$
- Compare:
- $f(-x) = f(x)$ so $f$ is even.
3. Function b) $f(x) = \\sin x + x$
- Compute $f(-x) = \\sin(-x) + (-x) = -\\sin x - x$
- Compute $-f(-x) = -(-\\sin x - x) = \\sin x + x$
- Compare:
- $f(-x)
eq f(x)$ and $-f(-x) = f(x)$ so $f$ is odd.
4. Function c) $f(x) = \frac{1}{x} - x$
- Compute $f(-x) = \frac{1}{-x} - (-x) = -\frac{1}{x} + x$
- Compute $-f(-x) = -(-\frac{1}{x} + x) = \frac{1}{x} - x$
- Compare:
- $f(-x)
eq f(x)$ and $-f(-x) = f(x)$ so $f$ is odd.
5. Function d) $f(x) = 2x^3 + x$
- Compute $f(-x) = 2(-x)^3 + (-x) = -2x^3 - x$
- Compute $-f(-x) = -(-2x^3 - x) = 2x^3 + x$
- Compare:
- $f(-x)
eq f(x)$ and $-f(-x) = f(x)$ so $f$ is odd.
6. Function e) $f(x) = 2x^2 - x$
- Compute $f(-x) = 2(-x)^2 - (-x) = 2x^2 + x$
- Compute $-f(-x) = -(2x^2 + x) = -2x^2 - x$
- Compare:
- $f(-x)
eq f(x)$ and $-f(-x)
eq f(x)$ so $f$ is neither even nor odd.
7. Function f) $f(x) = |2x + 3|$
- Compute $f(-x) = |2(-x) + 3| = |-2x + 3|$
- Usually $|2x+3| \neq |-2x+3|$ and $-f(-x) = -| -2x + 3|$ which is negative whereas $f(x)$ is non-negative
- So $f(-x) \neq f(x)$ and $-f(-x) \neq f(x)$, function is neither even nor odd.
Final answers:
- a) even
- b) odd
- c) odd
- d) odd
- e) neither
- f) neither