y=lg(x/3) * lg(x/12)
=(lgx-lg3)(lgx-lg3-2lg2)
=(lgx-lg3)^2-2lg2(lgx-lg3)
=(lgx-lg3)^2-2lg2(lgx-lg3)+(lg2)^2-(lg2)^2
=(lgx-lg3-lg2)^2-(lg2)^2
=(lgx-lg3/2)^2-(lg2)^2
所以当x=3/2时y取最小值为-(lg2)^2
y=lg(x/3) * lg(x/12)
=(lgx-lg3)(lgx-lg3-2lg2)
=(lgx-lg3)^2-2lg2(lgx-lg3)
=(lgx-lg3)^2-2lg2(lgx-lg3)+(lg2)^2-(lg2)^2
=(lgx-lg3-lg2)^2-(lg2)^2
=(lgx-lg3/2)^2-(lg2)^2
所以当x=3/2时y取最小值为-(lg2)^2