题目应该是-3x²+5x+1吧?
若是这样,则原式=-3（x²-5/3x+25/36-25/36）+1=-3（x-5/6）²+25/12+1=-3（x-5/6）²+37/12
所以最大值是37/12..配方法的方法是 理出2次项与1次项,然后根据（a+b）²=a²+2ab+b²
求出常数项（即加一个数,再减去这个数）
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