Y
=sinX(cosX-(√3/3)sinX)
=sinXcoxX-(√3/3)sinX*sinX
=sin(2X)/2-(√3/3)(1-cox(2X))/2
=[sin(2X)+(√3/3)cox(2X)]/2-(√3/6)
=[sin(2X)+tan(30度)cox(2X)]/2-(√3/6)
=[sin(2X)cos(30度)+sin(30度)cox(2X)]/[2cos(30度)]-(√3/6)
=sin(2X+30度)/[2cos(30度)]-(√3/6)
=sin(2X+30度)/(√3)-(√3/6)
当2X+30度=90度+360K度
即X=(30+180K)度时,K为整数
Y取最大值
Y=1/(√3)-(√3/6)=√3/6