【導(dǎo)讀】你會(huì)用描點(diǎn)法畫二次函數(shù)y=x2的圖象嗎?如果有,交點(diǎn)坐標(biāo)是什么?你是如何知道的?觀察圖象,回答問(wèn)題:2xy?請(qǐng)你找出幾對(duì)對(duì)稱點(diǎn)?a>0時(shí),拋物線y=ax2在x軸的上方,它的開(kāi)口向上,并且向上無(wú)限伸展;對(duì)稱軸的右側(cè),y隨著x增大而減小,當(dāng)x=0時(shí),函數(shù)y的值最大.在對(duì)稱軸側(cè),y隨著x的增大而增大;在對(duì)稱軸側(cè),變化,才會(huì)有質(zhì)的進(jìn)步.