cos (900- β) + 2 sin β - 3 cos (900-β)=
=- 2 cos (900- β) + 2 sin β =
=- 2 cos (360*2+ β) + 2 sin β =
=- 2 cos (180+ β) + 2 sin β =
= 2 cos β+ 2 sin β =
= 2 (cos β+ sin β )=
cos (900- β) + 2 sin β - 3 cos (900-β)=
=- 2 cos (900- β) + 2 sin β =
=- 2 cos (360*2+ β) + 2 sin β =
=- 2 cos (180+ β) + 2 sin β =
= 2 cos β+ 2 sin β =
= 2 (cos β+ sin β )=