Properties and derivatives of Logarithm functions

Definition of logarithmic function: For any positive number a is not equal to 1, log base a x = inverse of a^x. The graph of y = log x can be obtained by reflecting the graph of y = a^x across the line y = x. since log x and a^x are inverses of one another, composing them in either order gives the identity function.

We can have some observations about the logarithmic functions. From the graph, we can see that Logarithmic function is defined for positive values only and hence its domain is positive real numbers. The range is set of all real numbers. The graph always passes through (1, 0). The graph is increasing as we move from left to right. In the fourth quadrant, the graph approaches y-axis (but never meets it). It is also clear that the graphs of log base a x and a^x are mirror images of each other if y = x is taken as a mirror line.

Properties of Logarithmic Functions:
For any number x > 0 and y > 0, properties of base a logarithms are:
Product rule: log xy = log x + log y,
Quotient rule: log x / y = log x – log y,
Reciprocal rule: log 1 / y = -log y,
Power rule: log x^y = y log x.

Derivative of Logarithmic Functions: We use the following properties in the differentiation of logarithmic functions.
d/dx(e^x) = e^x
d/dx (log x) = 1/x.

Inverse of logarithmic functions : Since ln x and e^x are inverses of one another, we have  e^ln x = x ( all x > 0 ) ln ( e^x ) = x( all x ).

Logarithmic functions examples: Suppose we have to  Evaluate d/dx log base 10 ( 3x + 1 ).
d/dx log base 10 ( 3x + 1 ) = ( 1 / ln 10 ) .
( 1 / ( 3x + 1 ) ) d / dx ( 3x + 1 ) = 3 / [ ( ln 10 ) ( 3x + 1 ) ].

Evaluate integral log base 2 x /x dx.
Solution: integral log base 2 x / x dx = ( 1 / ln 2 ) integral ln x / x = ( 1 / ln 2 ) integral u du = ( 1 / ln 2 ) ( u^2 / 2 ) + C
= ( 1 / ln 2 ) [ ( ln x )^2 / 2 ] + C = ( ln x )^2 / 2 ln 2 + C.