Question

If $\alpha ={685}^o,$ then $(\cos \alpha -\sin \alpha )$ is equivalent to

• A. $-\cos {35}^o-\sin {35}^o$
• B. $-\cos {35}^o+\sin {35}^o$
• C. $\cos {35}^o-\sin {35}^o$
• D. $\cos {35}^o+\sin {35}^o$

Answer 1

Answer: (D)

$\cos {35}^o+\sin {35}^o$

$\alpha =685$

$=180\times 4-35$

$=4\pi -35$

$\cos \alpha -\sin \alpha$

$=\cos (4\pi -35)-\sin (4\pi -35)$

$=\cos 35-\sin (-35)$

$=\cos 35+\sin 35$