对于求形如函数 y=x +px( p 0 )型的最值问题 ,如果我们能形似联想到三角公式tanα +1tanα =2sin2α,便会考虑实施三角代换x =ptanα ,使其转化成三角函数问题 .该代换架设了这类函数三角化的一座“桥” ,从而为该问题的求解提供了又一解题新通途 .例 1　求函数 y=x2 +7x2 +4 For the shape problem such as the function y=x +px( p 0 ), if we can think of the trigonometric formula tanα+1tanα =2sin2α, we will consider the implementation of trigonometric substitution x = ptanα to transform it into a triangle. Function problem. This substitution sets up a “bridge” that triangulates this type of function, thus providing another solution to the problem. NEW WAY. Example 1 Find function y=x2 +7x2 +4