sin390度+cos(-660度)+3tan405度-sin540度
=sin(360+30)+cos(660度)+3tan(360+45)-sin(360+180)
=sin30+cos(720-60)+3tan45+sin180
=1/2+1/2+3-0
=4
sin390度+cos(-660度)+3tan405度-sin540度
=sin(360+30)+cos(660度)+3tan(360+45)-sin(360+180)
=sin30+cos(720-60)+3tan45+sin180
=1/2+1/2+3-0
=4