Difference Quotients
1. **State the problem:** We are given the function $f(x) = -x^2 - 5x + 2$ and need to find various difference quotients.
2. **Difference Quotient Definition:** The difference quotient generally refers to expressions like $$\frac{f(x+h) - f(x)}{h}$$ and similar versions where increments or points vary.
3. **Calculate $f(x+h)$:**
$$f(x+h) = -(x+h)^2 - 5(x+h) + 2$$
$$= -(x^2 + 2xh + h^2) - 5x - 5h + 2$$
$$= -x^2 - 2xh - h^2 - 5x - 5h + 2$$
4. **Compute the difference quotient $$\frac{f(x+h) - f(x)}{h}$$:**
$$= \frac{(-x^2 - 2xh - h^2 - 5x - 5h + 2) - (-x^2 - 5x + 2)}{h}$$
$$= \frac{-x^2 - 2xh - h^2 - 5x - 5h + 2 + x^2 + 5x - 2}{h}$$
$$= \frac{-2xh - h^2 - 5h}{h}$$
$$= \frac{h(-2x - h - 5)}{h}$$
$$= -2x - h - 5$$
5. **Interpretation:**
The difference quotient simplifies to $$-2x - h - 5$$.
6. **Other common difference quotients:**
- $$\frac{f(x) - f(a)}{x - a}$$ for a fixed number $a$.
Calculate $f(a)$:
$$f(a) = -a^2 - 5a + 2$$
Compute difference quotient:
$$\frac{f(x) - f(a)}{x - a} = \frac{(-x^2 - 5x + 2) - (-a^2 - 5a + 2)}{x - a}$$
$$= \frac{-x^2 - 5x + 2 + a^2 + 5a - 2}{x - a}$$
$$= \frac{a^2 - x^2 + 5a - 5x}{x - a}$$
$$= \frac{(a - x)(a + x) + 5(a - x)}{x - a}$$
Note $a - x = -(x - a)$, so:
$$= \frac{-(x - a)(a + x) - 5(x - a)}{x - a}$$
$$= - (a + x) - 5 = -a - x - 5$$
7. **Summary:**
- The difference quotient $$\frac{f(x+h) - f(x)}{h}$$ equals $$-2x - h - 5$$.
- The difference quotient $$\frac{f(x) - f(a)}{x - a}$$ equals $$-a - x - 5$$.
These represent the average rate of change between points on the parabola defined by $f(x)$.