利用lg（m/n）=lgm-lgn化簡(jiǎn)Y=lg(x/3)lg(x/12)=(lgx-lg3)(lgx-lg12)=(lgx)^2-(lg3+lg12)lgx+lg3lg12把lgx看成一個(gè)整體設(shè)t=lgx則Y=t^2-(lg3+lg12)t+lg3lg12=t^2-(lg36)t+lg3lg12=t^2-(2lg6)t+lg3lg12開(kāi)口向上 對(duì)稱抽為...設(shè)t=lgx則Y=t^2-(lg3+lg12)t+lg3lg12=t^2-(lg36)t+lg3lg12=t^2-(2lg6)t+lg3lg12能否寫(xiě)成頂點(diǎn)式可以　　頂點(diǎn)式：y=a(x-h)^2+k 　　頂點(diǎn)坐標(biāo)：(h,k)頂點(diǎn)坐標(biāo)如圖所示代入就行了