Buktikan identitas trigonometri berikut. Sin α + sin 3α / cos α + cos 3α = tan 2α

Identitas Trigonometri.

[tex]\displaystyle \frac{\sin \alpha +\sin 3\alpha }{\cos \alpha +\cos 3\alpha }\\ =\frac{2\sin \left ( \frac{\alpha +3\alpha }{2} \right )\cos \left ( \frac{\alpha -3\alpha }{2} \right )}{2\cos \left ( \frac{\alpha +3\alpha }{2} \right )\cos \left ( \frac{\alpha -3\alpha }{2} \right )}\\ =\tan 2\alpha [/tex]