Question

Express as a trigonometric function of one angle. cos 140 cos 520 - sin 140 sin 520​

Answer 1

cos(300)

Explanation:

you must use the identity:

cos(a+b)=cos a cos b - sin a sin b

In this case a=140 and b=540. Hence, the answer is

cos(140+520)

or

cos(660)

However, it's about a round and a half to the circle,

hence, 660 is the same as 660-360=300.

Finally, the answer is cos(300)