#  Evaluate  (a) sin 30°(b) sin 150°  (c) sin 60°(d) sin 120°  (e) cos 40°(f) cos 140°  (c) cos 10°(d) cos 170°

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 Evaluate  (a) sin 30°(b) sin 150°  (c) sin 60°(d) sin 120°  (e) cos 40°(f) cos 140°  (c) cos 10°(d) cos 170°

 Evaluate  (a) sin 30°= 0.5(b) sin 150°= 0.5  (c) sin 60°= 0.866..(d) sin 120°=0.866..  (e) cos 40°=0.766..(f) cos 140°=-0.766..  (c) cos 10°=0.984..(d) cos 170°=-0.984..

 Note that the sine of an acute angle and its (obtuse) supplement are the same.

 That means that any sine rule problem involving the missing angle could have two answers (an acute and obtuse).

 Note that the sine of an acute angle and its (obtuse) supplement are the same.  That means that any sine rule problem involving the missing angle could have two answers (an acute and obtuse).  In this course we assume the acute-angled answer, unless the obtuse angled answer is specifically requested.

 Find the value of θ to the nearest degree if it is obtuse.

θ 22° 10 m 5 m

 Find the value of θ to the nearest degree if it is obtuse. θ 22° 10 m 5 m

 Find the value of θ to the nearest degree if it is obtuse.  But θ is obtuse.  Therefore θ = 180 – 48.52222..  ≈ 131° θ 22° 10 m 5 m

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