Bab 3: Trigonometri

$x^2+y^2=(x+y{)}^2-2xy$ $=(\cos A{)}^2-2(\frac{1}{2}{\sin }^{2}A)={\cos }^{2}A-{\sin }^{2}A=\cos 2A$

tan 300° = tan (360° − 60°) = −tan 60° = −√3

sin 45° = √2/2 cos 225° = cos (180° + 45°) = −√2/2 √2/2 + (−√2/2) = 0

cos A = −12/15 = −4/5 sin² A = 1 − cos² A = 1 − (16/25) = 9/25 sin A = −3/5 = −9/15

sin θ = 4/5 (kuadran II → cos negatif) cos θ = −3/5 tan θ = sin θ / cos θ = (4/5) / (−3/5) = −4/3