Soal Ujian Matematika IPS Kelas 12
Tahun 2018Soal Pilihan Ganda
23. Nilai dari cos 210°. sin 330° - cos 60° adalah ...
A. - 1/4 (2-√3)
B. - 3/4 (2-√3)
C. 0
D. 1/4 (2-√3)
E. 3/4 (2-√3)
Jawaban : A
cos 210° = cos (180 + 30)°
cos 210° = - cos 30
cos 210° = - 1/2 √3
sin 330° = sin (270 + 60)°
sin 330° = - cos 60°
sin 330° = - 1/2
cos 60° = 1/2
cos 210°. sin 330° - cos 60°
= ( - 1/2 √3) . (- 1/2) - 1/2
= 1/4 √3 - 1/2
= 1/4 (√3 - 2)
= - 1/4 (2-√3)
cos 210° = cos (180 + 30)°
cos 210° = - cos 30
cos 210° = - 1/2 √3
sin 330° = sin (270 + 60)°
sin 330° = - cos 60°
sin 330° = - 1/2
cos 60° = 1/2
cos 210°. sin 330° - cos 60°
= ( - 1/2 √3) . (- 1/2) - 1/2
= 1/4 √3 - 1/2
= 1/4 (√3 - 2)
= - 1/4 (2-√3)
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