Real-Valued Functions of a Real Variable and Their Graphs

1. Real-Valued Functions of a Real Variable and Their Graphs Lecture 43 Section 9.1 Wed, Apr 18, 2007

2. Functions • We will consider real-valued functions that are of interest in studying the efficiency of algorithms. • Power functions • Logarithmic functions • Exponential functions

3. Power Functions • A power function is a function of the form f(x) = xa for some real number a. • We are interested in power functions where a 0.

4. The Constant Function f(x) = 1

5. The Linear Function f(x) = x

6. The Quadratic Function f(x) = x2

7. The Cubic Function f(x) = x3

8. Power Functions xa, a 1 • The higher the power of x, the faster the function grows. • xa grows faster than xb if a > b.

9. The Square-Root Function

10. The Cube-Root Function

11. The Fourth-Root Function

12. Power Functions xa, 0 < a < 1 • The lower the power of x (i.e., the higher the root), the more slowly the function grows. • xa grows more slowly than xb if a < b. • This is the same rule as before, stated in the inverse.

13. x3 x2 x x Power Functions

14. 2x 3x x x2 Multiples of Functions

15. Multiples of Functions • Notice that x2 eventually exceeds any constant multiple of x. • Generally, if f(x) grows faster than cg(x), for any real number c, then f(x) grows “significantly” faster than g(x). • In other words, we think of g(x) and cg(x) as growing at “about the same rate.”

16. Logarithmic Functions • A logarithmic function is a function of the form f(x) = logbx where b > 1. • The function logbx may be computed as (ln x)/(ln b).

17. The Logarithmic Function f(x) = log2x

18. Growth of the Logarithmic Function • The logarithmic functions grow more and more slowly as x gets larger and larger.

19. x1/2 log2 x x1/3 f(x) = log2x vs. g(x) = x1/n

20. Logarithmic Functions vs. Power Functions • The logarithmic functions grow more slowly than any power function xa, 0 < a < 1.

21. x x log2 x f(x) = x vs. g(x) = x log2x

22. f(x) vs. f(x) log2x • The growth rate of log x is between the growth rates of 1 and x. • Therefore, the growth rate of f(x) log x is between the growth rates of f(x) and xf(x).

23. x2 x2 log2 x x x log2 x f(x) vs. f(x) log2x

24. Multiplication of Functions • If f(x) grows faster than g(x), then f(x)h(x) grows faster than g(x)h(x), for all positive-valued functions h(x). • If f(x) grows faster than g(x), and g(x) grows faster than h(x), then f(x) grows faster than h(x).

25. Exponential Functions • An exponential function is a function of the form f(x) = ax, where a > 0. • We are interested in power functions where a 1.

26. The Exponential Function f(x) = 2x

27. 4x 3x 2x The Exponential Function f(x) = 2x

28. Growth of the Exponential Function • The larger the base, the faster the function grows • ax grows faster then bx, if a > b > 1.

29. 2x f(x) = 2x vs. Power Functions (Small Values of x)

30. 2x x3 f(x) = 2x vs. Power Functions (Large Values of x)

31. Growth of the Exponential Function • Every exponential function grows faster than every power function. • ax grows faster than xb, for all a > 1, b > 0.

32. Rates of Growth of Functions • The first derivative of a function gives its rate of change, or rate of growth.

33. Rates of Growth of Power Functions

34. Rates of Growth of Logarithmic Functions

35. Rates of Growth of Exponential Functions