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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°

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Presentation on theme: " 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°"— Presentation transcript:

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2  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°

3  Evaluate  (a) sin 30°= 0.5(b) sin 150°= 0.5  (c) sin 60°= (d) sin 120°=  (e) cos 40°= (f) cos 140°=  (c) cos 10°= (d) cos 170°=

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

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

6  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.

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

8 θ 22° 10 m 5 m

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

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


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