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LOGARITHMS. Another way to play with EXPONENTS. DEFINITION. What is it…. A LOGARITHM IS AN EXPONENT. If x = b y then log b (x) = y. PROPERTIES. What makes a logarithm tick!. MULTIPLICATON ADDITION.
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LOGARITHMS Another way to play with EXPONENTS
DEFINITION What is it…
A LOGARITHM IS AN EXPONENT • If x = by then logb(x) = y
PROPERTIES What makes a logarithm tick!
MULTIPLICATON ADDITION • A major property of logarithms is that they map multiplication to addition, as a result of the identity bxx by = b(x + y) • which by taking logarithms becomes logb(bx x by) = logb(b(x + y)) = x + y = logb(bx) + logb(by)
TAKING THE LOG OF AN EXPONENT • If you take the log of a number with an exponent, the exponent becomes a coefficient! • logb(cp) = p logb(c)
NATURAL LOGARITHMS and COMMON LOGARITHMS • A logarithm can have any base • We will concentrate on 2 • Common Logs have a base of 10 • log104 is written as log 4 • Natural Logs have a base of e • e = 2.7182818… • Also called Euler’s Number after Leonhard Euler • loge4 is written as ln 4
EVEN MORE PROPERTIES More exponential behavior…
PRODUCTS • Multiplying becomes addition • logbmn = logbm + logbn • For example: log (3· 4) = log 3 + log 4
QUOTIENTS • Division becomes subtraction • logb = logbm - logbn • Example: log = log 4 – log3
TRY THIS… • log4(64y6)1/3 = ?
FINAL TRICKS A few more things to know…
HOW TO CALCULATE • Your calculator has a button for common and natural logs. • Other logs can use the following property: • log6 x = (log x)/(log 6)
TRANSFORMATIONS-TRANSLATION • Compare y = log x to y = log (x + 2) • Compare y = log x to y = (log x) + 2
TRANSFORMATIONS-DILATION • Compare y = log x to y = 2 log x