Sec 4.3 Laws of Logarithms Objective: To understand the laws of logarithms, including the change of base formula.
Laws of Logarithms Let a be a positive number, with a ≠ 1. Let A, B, and C be any real numbers with A > 0 and B > 0, then the following laws apply:
The logarithm of a product of numbers is the sum of the logarithms of the numbers. Ex. 1 Evaluate
The logarithm of a quotient of numbers is the difference of the logarithms of the numbers. Ex. 2 Evaluate
The logarithm of a power of a number is the exponent times the logarithm of the number. Ex. 3 Evaluate
Expanding and Combining Logarithmic Expressions Ex 4. Use the Laws of Logarithms to expand each expression.
Ex 5. Combine the following into a single logarithm. 3 log x + ½ log(x + 1)
Ex 6. Combing the following into a single logarithm. 3 ln s + ½ ln t – 4 ln(t2 + 1)
Change of Base
Ex 7. Use the Change of Base Formula and common or natural logarithms to evaluate each logarithm, correct to five decimal places. (a) log8 5 (b) log9 20
Solving an Exponential Equation Ex 8. Solve for x. Round to 3 decimal places.
Ex. 9 Solve for x. Round to 3 decimal places.
Ex 10. Solve for x. Round to 3 decimal places.
HW – Log Worksheet