利用lg（m/n）=lgm-lgn化简Y=lg(x/3)lg(x/12)=(lgx-lg3)(lgx-lg12)=(lgx)^2-(lg3+lg12)lgx+lg3lg12把lgx看成一个整体设t=lgx则Y=t^2-(lg3+lg12)t+lg3lg12=t^2-(lg36)t+lg3lg12=t^2-(2lg6)t+lg3lg12开口向上 对称抽为...设t=lgx则Y=t^2-(lg3+lg12)t+lg3lg12=t^2-(lg36)t+lg3lg12=t^2-(2lg6)t+lg3lg12能否写成顶点式可以　　顶点式：y=a(x-h)^2+k 　　顶点坐标：(h,k)顶点坐标如图所示代入就行了