韦达定理及逆定理是中学数学中的重要定理,应用十分广泛.同学们对韦达定理的应用有一定的了解,而对逆定理的应用则认识不足,甚至有的同学根本不了解,事实上逆定理的应用不亚于正定理,现通过例题加以说明.一、求最值例1已知x,y是实数,且x+y+z=5,xy+yz+zx=3,求z的最大值.解由已知等式,得 Weida’s theorem and inverse theorem are important theorems in middle school mathematics and they are widely used. Students have a certain understanding of the application of Vedic theorem, but the application of the inverse theorem is not well understood, and some students even do not understand it. The application of the upper inverse theorem is no less than that of the positive theorem, which is illustrated by the example. First, find the best value. Example 1 Given that x and y are real numbers, and x+y+z=5, xy+yz+zx=3, find The maximum value of z. The solution is given by the known equation