If a n = b (a > 0, and a≠ 1), then the number n is called the logarithm of b with a base, and it is denoted as n=log(a)b, and a is a subscript.

Where a is called "base number" and b is called "true number".

Accordingly, the function y=logaX is called logarithmic function. The domain of logarithmic function is (0, +∞). Zero and negative numbers have no logarithm.

Cardinal A is a constant, and its value range is (0, 1)∩( 1, +∞).

When a= 10, write: y=lgx common logarithm.

Write y=lnx when a=e is the base of natural logarithm.

For example: 2 3 = 8

Then log(2) 8 = 3.