Hi, got an identity I need to prove. [tex]\frac{(cos 3A - cos 7A)} / {(sin 7A+sin 3A)}=tan 2A[tex] Any help would be appreciated. Thanks in advance.
Last edited by jo74; Jun 8th 2009 at 09:43 AM.
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Last edited by alexmahone; Jun 8th 2009 at 08:42 PM.
Originally Posted by jo74 Hi, got an identity I need to prove. [tex]\frac{(cos 3A - cos 7A)}{(sin 7A+sin 3A)}=tan 2A[tex] Any help would be appreciated. Thanks in advance. $\displaystyle \frac{(cos 3A - cos 7A)}{(sin 7A+sin 3A)}=tan 2A$ try to solve it with these $\displaystyle sinx + siny = 2 sin(\frac{x+y}{2}) cos(\frac{x-y}{2})$ $\displaystyle cosx - cosy = -2 sin(\frac{x+y}{2}) sin(\frac{x-y}{2})$ note sin(-x) = - sin(x)
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