Page 32 - modul trigonometri bilingual

Example 2.2

Specify the following trigonometric values.

1. sin 150° + sin 300°
2. tan 240° − cos 570°
3. sin(−30°) cos(−60°)

Alternative Solutions

1. sin 150° + sin 300° = sin(180° − 30°) + sin (360° − 60°)

= sin 150° + (−sin 60°)

1 1
= − √3
2 2
1
= − (√3 − 1)
2

Other ways:

sin 150° + sin 300° = sin(90 ° + 60°) + sin (270° + 30°)

= cos 60° + (− cos 30°)

1 1
= − √3
2 2
1
= − (√3 − 1)
2
1
So, value sin 150° + sin 300° is − (√3 − 1)
2

2. tan 240° − cos 570° = tan(180° + 60°) − cos (360° + 120°)

= tan 60° − cos 120 °

= √3 − cos(180° + 30°)

= √3 − (cos 30°)

1
= √3 + √3
2
3
= √3
2

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