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Bab Trigonometri
Matematika SMA Kelas X

4] tan a = 4/5, 180° < a < 270° di kuadran III

tan a = 4/5 = y/x

r = √(x² + y²)
r = √(5² + 4²)
r = √(25 + 16)
r = √41

cos a = x/r = - 5/√41 = (- 5/41) √41

5] sin 90° + cos 150° - sin 210°
= 1 + (-1/2) √3 - (-1/2)
= 1 - 1/2 √3 + 1/2
= 3/2 - 1/2 √3
= 1/2 (3 - √3).