Page 36 - Ebook Trigonometri_Krisna Hasugian_MESP 2019
P. 36
Sum to Product Formulas
+ −
sin + sin = 2 sin ( ) cos ( )
2 2
+ −
sin − sin = 2 cos ( ) sin ( )
2 2
+ −
cos + cos = 2 cos ( ) cos ( )
2 2
+ −
cos − cos = −2 sin ( ) sin ( )
2 2
Example 37 Use the sum-to-product formula to change sin 70° − sin 30° into a
product
70° + 30° 70° − 30°
sin 70° − sin 30° = 2 cos ( ) sin ( ) = 2 cos 50° ⋅ sin 20°
2 2
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