Write the following expression in terms of θ \theta θ only. Use the identity for the cosine of a sum. cos ⁡ ( θ + π 2 ) \cos\left(\theta+\frac{\pi}{2}\right) cos ( θ + 2 π )

− sin ⁡ θ -\sin\theta − sin θ

− cos ⁡ θ -\cos\theta − cos θ

cos ⁡ 2 θ \cos2\theta cos 2 θ

− 2 sin ⁡ θ -2\sin\theta − 2 sin θ

6. Trigonometric Identities and More Equations

6. Trigonometric Identities and More Equations / Sum and Difference Identities / Problem 9

Write the following expression in terms of $\theta$ only. Use the identity for the cosine of a sum.
$\cos\left(\theta+\frac{\pi}{2}\right)$

$-\cos\theta$

$-\sin\theta$

$\cos2\theta$

$-2\sin\theta$