Question

Use an Addition or Subtraction Formula to write the expression as a trigonometric function of one number.
cos 10° cos 80° − sin 10° sin 80°

also the exact answer

Answer 1

\[\large\rm \cos\color{indianred}{A}\cos\color{royalblue}{B}-\sin\color{indianred}{A}\sin\color{royalblue}{B}\quad=\quad \cos(\color{indianred}{A}+\color{royalblue}{B})\]

Answer 2

\[\large\rm \cos\color{indianred}{10}\cos\color{royalblue}{80}-\sin\color{indianred}{10}\sin\color{royalblue}{80}\quad=\quad ?\]

Answer 3

@cailindevereux

Look at the identity posted by @zepdrix


Answer this:

If A = 10° and B = 80°, then A + B = what?

Answer 4

After you get the sum of A and B, what is the value of the cosine of that number of degrees?