## Trigonometry (11th Edition) Clone

$$\cos300^\circ=\cos^2150^\circ-\sin^2150^\circ$$ 25 is matched with F.
$$\cos300^\circ$$ We rewrite $300^\circ$ as double the angle $150^\circ$. In detail, $$\cos300^\circ=\cos(2\times150^\circ)$$ This fact points to the use of the double identity for cosine, which states $$\cos(2A)=\cos^2A-\sin^2A$$ Therefore, for $A=150^\circ$: $$\cos300^\circ=\cos^2150^\circ-\sin^2150^\circ$$ The equation indicates that 25 should be matched with F.