= cos (105˚ - 75˚) – cos (105˚ + 75˚)
= cos 30˚ - cos 180˚
= ½ √3 – (-1)
= ½ √3 + 1
2. Buktikan bahwa: 2 cos (x˚ + 105˚) sin (x˚ + 75˚) = - (1/2 + sin 2x˚)
Jawaban:
2 cos (x˚ + 105˚) sin (x˚ + 75˚)
= sin [(x˚ + 105˚) + (x˚ + 75˚)] - sin [(x˚ + 105˚) - (x˚ + 75˚)]
= sin (x˚ + 105˚ + x˚ + 75˚) – sin (x˚ + 105˚ - (x˚ - 75˚)
= sin (2x˚ + 180˚) – sin (30˚)
= sin (2x + 180˚) – ½
Penulis | : | Ratnaningtyas Winahyu |
Editor | : | Ratnaningtyas Winahyu |
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