## Trigonometry (11th Edition) Clone

$$\cos^2\frac{\pi}{6}-\sin^2\frac{\pi}{6}=\frac{1}{2}$$ 4 would be matched with A.
$$X=\cos^2\frac{\pi}{6}-\sin^2\frac{\pi}{6}$$ From the double-angle identities: $$\cos^2 A-\sin^2 A=\cos2A$$ Thus $X$ can be seen here as $\cos^2 A-\sin^2 A$ with $A=\frac{\pi}{6}$. Therefore, $$X=\cos\Big(2\times\frac{\pi}{6}\Big)$$ $$X=\cos\frac{\pi}{3}$$ $$X=\frac{1}{2}$$ So, $$\cos^2\frac{\pi}{6}-\sin^2\frac{\pi}{6}=\frac{1}{2}$$ 4 would be matched with A.