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education/math/MATH1060 (trig)/Double and Half Angle Identities.md

@@ -1,2 +1,10 @@
+# Double Angle Identities
 $$ \sin(2\theta) = 2\sin\theta\cos\theta $$
-$$ \cos(2\theta) = \cos^2\theta - \sin^2
+$$
+\begin{matrix}
+\cos(2\theta) = \cos^2\theta - \sin^2\theta\\
+= 1 - 2sin^2\theta\\
+= 2cos^2\theta - 1\\
+\end{matrix}
+$$
+$$ \tan(2\theta) = \dfrac{2\tan\theta}{1-\tan^2\theta}$$