52 lines
3.2 KiB
Markdown
52 lines
3.2 KiB
Markdown
You are setting yourself up perfectly for Exam 1 by reviewing this material before jumping into the homework!
|
|
|
|
I have reviewed the PowerPoint you uploaded. The absolute best news about this entire chapter is that **there is almost no new math here**. It is actually just a classic Algebra 1 concept wearing a sophisticated Calculus disguise.
|
|
|
|
Here is your "Cheat Code" breakdown of the Average Rates of Change module to add to your study guide.
|
|
|
|
---
|
|
|
|
# Average Rates of Change & The Difference Quotient
|
|
|
|
### The Big Secret: It is Just the Slope Formula!
|
|
In Algebra 1, you learned how to find the slope of a straight line using the formula $m = \frac{y_2 - y_1}{x_2 - x_1}$.
|
|
|
|
In Calculus, we don't just deal with straight lines; we deal with curves. [cite_start]To find the "average" slope between two specific points on a curve, we draw a straight line connecting them[cite: 249].
|
|
* [cite_start]**The Secant Line:** The straight line connecting two points on a curve is called a secant line[cite: 169, 252].
|
|
* [cite_start]**The Formula:** The average rate of change is simply the slope of that secant line[cite: 168, 254]. We just write the slope formula in function notation:
|
|
[cite_start]$$\frac{f(x_2) - f(x_1)}{x_2 - x_1}$$ [cite: 160]
|
|
|
|
|
|
---
|
|
|
|
### Homework Problem Type 1: The Number Cruncher
|
|
[cite_start]The homework will give you an equation and an interval, like "Find the average rate of change for $f(x) = x^2$ as $x$ changes from 1 to 3." [cite: 171, 172, 173]
|
|
|
|
**Your Cheat Code Steps:**
|
|
1. **Find $y_1$:** Plug the first $x$-number into the equation. (e.g., $1^2 = 1$).
|
|
2. **Find $y_2$:** Plug the second $x$-number into the equation. (e.g., $3^2 = 9$).
|
|
3. **Do the Slope Math:** Plug everything into the slope formula: $\frac{9 - 1}{3 - 1} = \frac{8}{2} = 4$.
|
|
|
|
---
|
|
|
|
### The Boss Battle: The Difference Quotient
|
|
This is the second half of the lesson, and it is the exact same concept, just written differently. [cite_start]Instead of calling our two points $x_1$ and $x_2$, we call our first point $x$, and we say our second point is $h$ steps away[cite: 251]. Therefore, the second point is $(x + h)$.
|
|
|
|
If you plug those into the slope formula, you get the **Difference Quotient**:
|
|
[cite_start]$$\frac{f(x + h) - f(x)}{h}$$ [cite: 219, 220]
|
|
|
|
### Homework Problem Type 2: The Algebraic Simplifier
|
|
[cite_start]The homework will ask you to "find a simplified form of the difference quotient" for an equation[cite: 234, 244]. [cite_start]It is highly recommended to simplify the difference quotient algebraically *before* evaluating it for specific numbers[cite: 256].
|
|
|
|
**Your Cheat Code Steps:**
|
|
Let's use the equation $f(x) = x^2$ as an example.
|
|
1. **Build the Front Part $f(x+h)$:** Replace every $x$ in the original equation with $(x+h)$ and expand it using FOIL.
|
|
* $(x+h)^2 = x^2 + 2xh + h^2$
|
|
2. **Subtract the Original Equation:** Subtract the original $f(x)$ from what you just built.
|
|
* $x^2 + 2xh + h^2 - x^2$
|
|
* *Self-Check:* At this step, everything that does NOT have an $h$ attached to it should cancel out perfectly! (The $x^2$ and $-x^2$ cancel).
|
|
3. **Divide by $h$:** Divide whatever is left by $h$.
|
|
* $\frac{2xh + h^2}{h}$
|
|
* Factor an $h$ out of the top and cross it out with the bottom $h$.
|
|
* **Final Answer:** $2x + h$
|