Section 2.3 – The Product and Quotient Rules and Higher-Order Derivatives

1. Section 2.3 – The Product and Quotient Rules and Higher-Order Derivatives

2. The Product Rule Another way to write the Rule: The derivative of a product of functions is NOT the product of the derivatives. If f and gare both differentiable, then In other words, the derivative of a product of two functions is the first function times the derivative of the second function plus the second function times the derivative of the first function.

3. Example 1 u v v u' u v' Product Rule Sum/Difference Rule Power Rule Simplify Differentiate the function:

4. Example 2 u v Find the derivative: u v' u v' Product Rule Evaluate the derivative: If h(x) = xg(x) and it is known that g(3) = 5 and g'(3) =2, find h'(3).

5. The Quotient Rule “Lo-d-Hi minus Hi-d-Lo” Another way to write the Rule: The derivative of a quotient of functions is NOT the quotient of the derivatives. If f and gare both differentiable, then In other words, the derivative of a quotient is the denominator times the derivative of the numerator minus the numerator times the derivative of the denominator, all divided by the square of the denominator.

6. Example 1 u v v u v' u' v2 Quotient Rule Differentiate the function:

7. Example 2 Find the derivative (slope of the tangent line) when x=1 Use the point-slope formula to find an equation Find the Derivative Find an equation of the tangent line to the curve at the point (1,½).

8. Example 3 The Quotient Rule is long, don’t forget to rewrite if possible. Rewrite to use the power rule Sum and Difference Rules Constant Multiple Rule Power Rule Try to find the Least Common Denominator Simplify Differentiate the function:

9. More Derivatives of Trigonometric Functions We will assume the following to be true:

10. Example 1 Use the Quotient Rule u v u' v u v' Quotient Rule Always look to simplify Trig Law: 1 + tan2 = sec2 Differentiate the function:

11. Example 2 Use the Product Rule u v u v' v u' Product Rule Differentiate the function:

12. Example 1 Let a. Find the derivative of the function.

13. Example 1 (Continued) Let b. Find the derivative of the function found in (a).

14. Example 1 (Continued) Let c. Find the derivative of the function found in (b).

15. Example 1 (Continued) Let d. Find the derivative of the function found in (c).

16. Example 1 (Continued) We have just differentiated the derivative of a function. Because the derivative of a function is a function, differentiation can be applied over and over as long as the derivative is a differentiable function. Let e. Find the derivative of the function found in (d).

17. Higher-Order Derivatives: Notation Notice that for derivatives of higher order than the third, the parentheses distinguish a derivative from a power. For example: . First Derivative: Second Derivative: Third Derivative: Fourth Derivative: nth Derivative:

18. Example 1 (Continued) You should note that all higher-order derivatives of a polynomial p(x) will also be polynomials, and if p has degree n, then p(n)(x) = 0 for k ≥ n+1. Let f. Define the derivatives from (a-e) with the correct notation.

19. Example 2 Find the first derivative: Find the second derivative: Find the third derivative: No higher-order derivative will equal 0 since the power of the function will never be 0. It decreases by one each time. If , find . Will ever equal 0?

20. Example 3 Find the first derivative: Find the second derivative: Find the second derivative of .

21. Average Acceleration Acceleration is the rate at which an object changes its velocity. An object is accelerating if it is changing its velocity. v(t) Find the average rate of change of velocity for times that are close and enclose time 5. 2 t 1 2 3 4 5 6 -2 -4 Example: Estimate the velocity at time 5 for graph of velocity at time t below.

22. Instantaneous Acceleration If s = s(t) is the position function of an object that moves in a straight line, we know that its first derivative represents the velocity v(t) of the object as a function of time. The instantaneous rate of change of velocity with respect to time is called the acceleration a(t) of an object. Thus, the acceleration function is the derivative of the velocity function and is therefore the second derivative of the position function.

23. Position, Velocity, and Acceleration Units = Measure of length (ft, m, km, etc) The object is… Moving right/up when v(t) > 0 Moving left/down when v(t) < 0 Still or changing directions when v(t) = 0 Units = Distance/Time (mph, m/s, ft/hr, etc) Speed = absolute value of v(t) Units = (Distance/Time)/Time (m/s2) Position, Velocity, and Acceleration are related in the following manner: Position: Velocity: Acceleration:

24. Example v(t) 2 t 1 2 3 4 5 6 -2 -4 Example: The graph below at left is a graph of a particle’s velocity at time t. Graph the object’s acceleration where it exists and answer the questions below Positive acceleration and positive velocity Constant a(t) Moving towards the x-axis. Corner Positive acceleration and Negative velocity m = 0 2 m = -4 t 1 2 3 4 5 6 m = 2 Moving away from x-axis. -2 0 acceleration and 0 velocity m = 4 -4 Negative acceleration and Negative velocity Negative acceleration and Positive velocity (0,2) U (5,6) When is the particle speeding up? When is the particle traveling at a constant speed? When is the function slowing down? (2,4) (4,5) U (6,7)

25. Speeding Up and Slowing Down An object is SPEEDING UP when the following occur: • Algebraic: If the velocity and the acceleration agree in sign • Graphical: If the curve is moving AWAY from the x-axis An object is traveling at a CONSTANT SPEED when the following occur: • Algebraic: Velocity is constant and acceleration is 0. • Graphically: The velocity curve is horizontal An object is SLOWING DOWN when the following occur: • Algebraic: Velocity and acceleration disagree in sign • Graphically: The velocity curve is moving towards the x-axis

26. Example 1 v(t) 2 t 1 2 3 4 5 6 -2 -4 The velocity of a particle moving left and right with respect to an origin is graphed below. Complete the following: • Find the average acceleration between time 2 and time 6. • Graph the particle’s acceleration where it exists. • Describe the particles speed.

27. Example 2 Sketch a graph of the function that describes the velocity of a particle moving up and down with the following characteristics: The particle’s velocity is defined on [0,8] The particle is only slowing down on (1,3)U(4,7) The acceleration is never 0.

28. Example 3 The derivative of the velocity function is the acceleration function. The derivative of the position function is the velocity function. The position of a particle is given by the equation where t is measured in seconds and s in meters. (a) Find the acceleration at time t.

29. Example 3 (continued) m/s2 Since the velocity and acceleration agree in signs, the particle is speeding up. m/s m/s2 The position of a particle is given by the equation where t is measured in seconds and s in meters. (b) What is the acceleration after 4 seconds? (c) Is the particle speeding up, slowing down, or traveling at a constant speed at 4 seconds?

30. Example 3 (continued) – + + Velocity: Speeding Up: (1,2) U (3,∞) Slowing Down: (0,1) U (2,3) The position of a particle is given by the equation where t is measured in seconds and s in meters. (d) When is the particle speeding up? When is it slowing down? Acceleration: – +