The applicable conditions for finding the maximum value of universal K method need to meet the following two points at the same time: (1) means that there is a quadratic term in the constraint condition. (2) The objective function is a linear function. Generally used to find the maximum value of basic inequality.

The process of finding the maximum value by universal K method is very simple. First, set the objective function to k, then use x to represent y or y to represent x, and then substitute the constraint conditions to get a quadratic equation with one variable about x or y. Because the constraint condition is established in the real number range, the obtained unary quadratic equation is the real number root, that is, the discriminant is greater than or equal to zero, thus an inequality about k is obtained, and finally the maximum value of the objective function can be obtained by solving this inequality.

Basic inequality is an inequality that is mainly used to find the maximum value of some functions and prove it. It means that the arithmetic mean of two positive real numbers is greater than or equal to their geometric mean.

When using basic inequalities, we should keep in mind the seven-character mantra of "one positive", "two definite" and "third class". "One positive" means that both formulas are positive numbers, "two definite" means that the sum or product is constant when the basic inequality is applied to find the maximum value, and "three-phase equality" means that if and only if the two formulas are equal, they can be equal. Basic inequality is an important test point of high school mathematics. Generally speaking, it is not difficult to test, and it is a knowledge point that high school students must master.