Question

Use a sum or difference formula (not a calculator or computer!) to determine the value of cos(7π/12).
a. (√2)/4+(√6)/4
b. 5/6
c. (√2)/4-(√6)/4
d. (√3)/4

Answer 1

\[\frac{\pi}{3}+\frac{\pi}{4}=\frac{7\pi}{12}\]

Answer 2

\[\cos(\alpha +\beta)=\cos(\alpha)\cos(\beta)-\sin(\alpha)\sin(\beta)\] put \(\alpha =\frac{\pi}{3}, \beta=\frac{\pi}{4}\)

Answer 3

Would it be C?

Answer 4

yeah as usual it is C

Answer 5

I used a calculator, would the answer be different if I didn't use one?