Logarithm: if a x = n(a >；; 0, and a≠ 1), then the number x is called the logarithm of n with a base, and it is denoted as x=log(a)N, where a is called the base of logarithm, n is called real number, and a >；; O and a≠ 1, n >；; 0, and the logarithm is in the real number range, negative numbers and 0 have no logarithm, and in the complex number range, negative numbers have logarithm. Because mathematics is a mathematical model established to serve real life, it must exist in reality, so there is no mathematical model with negative real numbers in real life. Therefore, the case of negative real numbers in higher mathematics is only theoretically established. Logarithmic addition formula: two logarithms are added with the same base, which is simplified into a formula first and then solved. Because the real number is greater than 0, there is a solution, so less than 0 is an empty set. If it is not the same base, you need to find two domains first, and then add them according to the logarithm of the same base, and multiply them by the real number with the same base. The number of different bases can be calculated by changing the base formula to the re-addition step of the same base.