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Exponential Functions

Exponential Functions. An exponential function is of the form f ( x ) = a x , where a > 0. a is called the base . Ex. Let h ( x ) = 3.1 x , evaluate h (-1.8). Ex. Sketch f ( x ) = 2 x and g ( x ) = 4 x. Ex. Sketch f ( x ) = 2 - x and g ( x ) = 4 - x.

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Exponential Functions

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  1. Exponential Functions An exponential function is of the form f (x) = a x, where a > 0. a is called the base. Ex. Let h(x) = 3.1x, evaluate h(-1.8).

  2. Ex. Sketch f (x) = 2x and g(x) = 4x

  3. Ex. Sketch f (x) = 2-x and g(x) = 4-x

  4. Note that every exponential function has • Domain of all reals • Range of y > 0 • Horizontal asymptote at y = 0 Because they are monotonic, these functions are one-to-one Let a > 0 and a≠ 1. If ax = ay, then x = y.

  5. Ex. Solve for x. a) 9x = 3x + 1 b) (½)x = 8

  6. Ex. Sketch the graph of f (x) = 1 – 3x.

  7. The number e≈ 2.718281828 is called the natural base and the function f (x) = ex is called the natural exponential function. We will see this function come up in some application problems, especially investment problems where interest is compounded continuously. Ex. Let f (x) = ex, evaluate f (3.2)

  8. Ex. Use a calculator to graph f (x) = 2e.24x and

  9. When interest is compounded n times per year, we used the formula If interest is compounded continually, we use the formula

  10. Ex. You invest $12,000 at an annual rate of 9%. How much more can you make in 5 years if interest is compounded continually rather than monthly?

  11. Ex. After the Chernobyl nuclear accident in 1986, the amount remaining after t years from a 10 pound sample of plutonium can be modeled by the function How much of this 10 pound sample remains today?

  12. Practice Problems Section 5.1 Problems 1, 11, 13, 35, 45, 61, 67

  13. Logarithmic Functions We saw that exponential functions are invertible. The logarithmic functionf (x) = logax is the inverse function of g(x) = ax. y = logax ↔ x = ay

  14. Ex. Evaluate by hand. a) log232 b) log31 c) log93 d) log10

  15. The logarithmic function with base 10 is called the common logarithm is can be written f (x) = log x Ex. Given the function f (x) = log x, evaluate f (2.5) and f (-2).

  16. Ex. Use the graph of f (x) = 2x to sketch g(x) = log2x.

  17. Note that every logarithmic function has • Domain of x > 0 • Range of all reals • Vertical asymptote at x = 0

  18. Ex. Sketch the graph of f (x) = 1 – log x

  19. Properties of Logarithms a0 = 1 ↔ loga1 = 0 a1 = a ↔ logaa = 1 Since exponents and logarithms are inverse, Since logarithms are one-to-one, we know: If logax = logay, then x = y.

  20. Ex. Simplify a) log41 b) log88 c) log6620

  21. Ex. Solve a) log34x = log320 b) log (2x + 1) = log x

  22. The function f (x) = logex is called the natural logarithm function, and it is often written f (x) = ln x Ex. Evaluate the natural log function at x = 3 and x = -4

  23. Ex. Simplify a) ln b) ln e5 c) 8ln 1 d) 2ln e

  24. Ex. Identify the domain a) f (x) = ln(x – 2) b) f (x) = ln(2 – x) c) f (x) = ln(x2)

  25. Practice Problems Section 5.2 Problems 17, 23, 27, 31, 39, 65, 79

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