Question #a451b

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Question #a451b

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Answer 1 · 2017-06-15T13:42:17

$cos (210) = - \frac{\sqrt{3}}{2}$ $cos(210)=-sqrt3 /2$

Explanation:

$cos (210) = cos (180 + 30)$ $cos (210)=cos (180+30)$
$cos (a + b) = cos a \cdot cos b - sin a \cdot sin b$ $cos(a+b)=cos a*cos b-sin a*sin b$
$cos (210) = cos (180) \cdot cos (30) - sin (180) \cdot sin (30)$ $cos(210)=cos(180)*cos(30)-sin(180)*sin(30)$
$cos (180) = - 1$ $cos(180)=-1$
$cos (30) = \frac{\sqrt{3}}{2}$ $cos(30)=sqrt 3/2$
$sin (180) = 0$ $sin(180)=0$
$sin (30) = \frac{1}{2}$ $sin(30)=1/2$
$cos (210) = cos (180) \cdot cos (30) - sin (180) \cdot sin (30)$ $cos(210)=cos(180)*cos(30)-sin(180)*sin(30)$
$cos (210) = - 1 \cdot \frac{\sqrt{3}}{2} - 0 \cdot \frac{1}{2}$ $cos(210)=-1*sqrt 3/2-0*1/2$
$cos (210) = - \frac{\sqrt{3}}{2} - 0$ $cos(210)=-sqrt 3/2-0$
$cos (210) = - \frac{\sqrt{3}}{2}$ $cos(210)=-sqrt3 /2$

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Question #a451b

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