mac1140_lecture24_1

# mac1140_lecture24_1 - L24 5.4 Evaluating Logs and Changing...

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210 L24 §5.4 Evaluating Logs and Changing Base Calculators can be used to evaluate base e or base 10 logarithms. Notation : 10 log log xx = Example : We use a calculator to find log142 2.1523 ln10 2.3026 Example : Calculate 3 log 5 . Let's change log ln a x x . log a yx = Thus, ln log a x x a = . So, 3 ln5 log 51 . 4 6 5 0 ln3 =≈

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211 Change-of-Base Theorem: For any positive real numbers , , and xa b , where 1 and 1 ab ≠≠ : log log log b a b x x a = . Example : Compute: = 20 log 6 = 5 log 16
212 §5.5 Exponential and Logarithmic Equations Recall the procedure of solving an exponential equa t ion : 2 35 3 2 x + = If it is possible , we write each side as a power of the same base and use the property of exponents: xy aa x y =⇔ = (0 ,1 ) >≠ The more general method of solving exponential equations is the following: To solve an exponential equation: 1. Reduce an equation to one of the forms () fx ab = , f xg x = , f x = 2. Compose logarithmic function to both sides (it brings down the exponents with the variable). 3. Simplify and solve for the variable.

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213 Example . Solve each equation: a) 500 300 x e = b) 2 52 t =
214 c) 52 28 a e + = d) 4 0.08 100 1 221 4 t ⎛⎞ +=

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mac1140_lecture24_1 - L24 5.4 Evaluating Logs and Changing...

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