Monotonicity - All Important Formulas and Concepts
Monotonicity Basics:
Monotonicity tells us where a function is increasing or decreasing.
1. Definition:
- A function f(x) is:
- Increasing in an interval if f'(x) > 0
- Decreasing in an interval if f'(x) < 0
- Constant if f'(x) = 0
Formulas and Rules:
2. First Derivative Test (Monotonicity):
Used to check where the function is increasing/decreasing.
- If f'(x) > 0 in an interval => f(x) is increasing
- If f'(x) < 0 in an interval => f(x) is decreasing
3. Critical Points:
Points where:
- f'(x) = 0 or
- f'(x) is undefined
Use these to split the domain and test sign of f'(x).
4. Intervals of Monotonicity:
- Find critical points of f'(x)
- Use number line method to test sign of f'(x) in each interval
- Positive => Increasing; Negative => Decreasing
5. Behavior Summary:
- If f'(x) changes from + to - at a point => local maximum
- If f'(x) changes from - to + => local minimum
6. Application:
- Helps in curve sketching, finding turning points, optimization
7. Higher Order Derivatives (Optional):
If f''(x) > 0 => f(x) is concave upward (but not necessarily increasing)
If f''(x) < 0 => f(x) is concave downward
Tip:
Always draw a sign chart of f'(x) to make analysis easier.