$\tan \left(\alpha-\frac{\pi}{4}\right), \sin \left(\frac{\pi}{6}+\alpha\right) ; \quad \cot \alpha=\frac{1}{2}, \pi<\alpha<\frac{3}{2} \pi$
$\tan \left(\alpha-\frac{\pi}{4}\right), \sin \left(\frac{\pi}{6}+\alpha\right) ; \quad \cot \alpha=\frac{1}{2}, \pi<\alpha<\frac{3}{2} \pi$
pi < α < 3/2·pi angolo del 3° quadrante
SENO<0; COSENO<0; TANGENTE>0; COTANGENTE>0
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COT(α) = 1/2
TAN(α - pi/4) = (TAN(α) - TAN(pi/4))/(1 + TAN(α)·TAN(pi/4))
TAN(α - pi/4) = (TAN(α) - 1)/(TAN(α) + 1)
TAN(α) = 1/COT(α)=2
TAN(α - pi/4) = (2 - 1)/(2 + 1) = 1/3
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SIN(pi/6 + α) = SIN(pi/6)·COS(α) + SIN(α)·COS(pi/6)
SIN(pi/6 + α) = 1/2·COS(α) + SIN(α)·(√3/2)
TAN(α) = 2 = SIN(α)/√(1 - SIN(α)^2))
pongo SIN(α) = y ed elevo alquadrato:
4 = y^2/(1 - y^2)------> y = - 2·√5/5 ∨ y = 2·√5/5 ho scelto la negativa (3°Q)
SIN(α) = - 2·√5/5
COS(α) = - √(1 - (- 2·√5/5)^2)------>COS(α) = - √5/5
SIN(pi/6 + α) = 1/2·(- √5/5) + (- 2·√5/5)·(√3/2)
SIN(pi/6 + α) = - √5/10 +( - √15/5)
SIN(pi/6 + α) = - √5·(2·√3 + 1)/10