-2x²+50x+1200什=-2(x²-25x)+1200=-2(x²-25x+625/4)+625/2+1200=-2(x-25/2)²+3025/2当x=25/2时,-2x²+50x+的值最大(=3025/2)
-2x²+50x+1200=-2(x²-25x+625/4)+1200+625/2=-2(x-25/2)²+1512.5当x=25/2时最大，最大值是1512.5
