sin 420 degrees . cos 390 degrees - cos (- 330 degrees). sin (-300 degrees) =?
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sin 420 = sin (360+60)= sin 60
cos 390 = cos (360+30) = cos 30
cos (-330) = cos 330= cos (360-30) = cos 30
sin(-300)= - sin 300 = - sin(360-60) = sin 60
given
sin 420 cos 390 - cos (-330) sin(-300)
= sin 60 cos 30 - cos 30 sin 60
= 0
cos 390 = cos (360+30) = cos 30
cos (-330) = cos 330= cos (360-30) = cos 30
sin(-300)= - sin 300 = - sin(360-60) = sin 60
given
sin 420 cos 390 - cos (-330) sin(-300)
= sin 60 cos 30 - cos 30 sin 60
= 0
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