High school mathematics separation variable method
Variable separation is to arrange an unknown variable and other known variables in an inequality (or equation) on both sides of the inequality (or equal sign) respectively. For example, when x belongs to [1/3,3], there is always ln(x+a)≥x, and the range of a is found. It can be sorted as a ≥ e x-x, which is variable separation. Of course, it is only necessary to make a greater than or equal to the maximum value of the right "function" f (x) = e x-x, [1/3,3]; Therefore, the problem is transformed into the problem of finding the maximum value of the function in the closed interval.