Math Doubts

Logarithmic identities


Log One Rule

Logarithm of one to any number is zero.

$\large \log_{b}{1} = 0$


Log of base Rule

Logarithm of any number to same number is one.

$\large \log_{b} b = 1$


Fundamental Law

$\large b^{\displaystyle \log_{b} m} = m$


Product Law

Logarithm of the product of two or more numbers to a base is sum of the logarithm of each number to same base.

$\large (1). \,\,\,\,\,\,$ $\large \log_{b} (m.n) =$ $\large \log_{b} m + \log_{b} n$

$\large (2). \,\,\,\,\,\,$ $\large \log_{b} (m.n.o \cdots)$ $\large =$ $\large \log_{b} m +$ $\large \log_{b} n +$ $\large \log_{b} o + \cdots$


Quotient Rule

Logarithm of quotient of two numbers to a base is the subtraction of logarithm of a number from logarithm of another number.

$\large \log_{b} \Big(\dfrac{m}{n}\Big) = \log_{b} m \,–\, \log_{b} n$


Power Rule

$\large (1). \,\,\,\,\,\, $ $\large \log_{b} m^n = n \log_{b} m$

$\large (2). \,\,\,\,\,\, $ $\large \log_{b^y} m = \dfrac{1}{y} \log_{b} m$

$\large (3). \,\,\,\,\,\, $ $\large \log_{b^y} m^x = \dfrac{x}{y} \log_{b} m$


Change of Base formulas

$\large (1). \,\,\,\,\,\, $ $\large \log_{b}{m} = \log_{d}{m} \times \log_{b}{d}$

$\large (2). \,\,\,\,\,\, $ $\large \log_{b}{m} = \dfrac{\log_{d}{m}}{\log_{d}{b}}$

$\large (3). \,\,\,\,\,\, $ $\large \log_{b}{m} = \dfrac{1}{\log_{m}{b}}$

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