Section 5 Mathematical Formulas

5-1 Trigonometric Function

5-1-8 Product-of sum Formula

$sin\theta \pm sin\phi=2sin(\frac{\theta \pm \phi}{2})cos(\frac{\theta \mp \phi}{2})$

$cos\theta+cos\phi=2cos(\frac{\theta+\phi}{2})cos(\frac{\theta-\phi}{2})$

$cos\theta-cos\phi=-2sin(\frac{\theta+\phi}{2})sin(\frac{\theta-\phi}{2})$

　　　　　

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