Answer: cos(76)
=========================================================
Explanation:
The original expression is of the pattern cos cos + sin sin. This pattern matches the second identity in the hint. Specifically, we'll say the following:
cos(A - B) = cos(A)cos(B) + sin(A)sin(B)
cos(A)cos(B) + sin(A)sin(B) = cos(A - B)
cos(94)cos(18) + sin(94)sin(18) = cos(94 - 18)
cos(94)cos(18) + sin(94)sin(18) = cos(76)
----------
We can verify this by use of a calculator. Make sure your calculator is in degree mode.
- cos(94)cos(18) + sin(94)sin(18) = 0.24192
- cos(76) = 0.24192
Both expressions give the same decimal approximation, so this helps confirm the two expressions are equal. You could also use the idea that if x = y, then x-y = 0. Through this method, you'll subtract the left and right hand sides and you should get (very close to) zero.
