Question

find the exxact value of the following: cos(105degrees)

Answer 1

find 105 degrees on the unit circle of the attached cheat sheet
the first coordinate is cosine

Answer 2

ok that doesn't work, does it
we have to do something else

Answer 3

recognizing that
\[105=60+45\] you can use the addition angle formula for cosine

Answer 4

\[\cos(105)=\cos(60+45)\\
\cos(60+45)=\cos(60)+\cos(45)-\sin(60)\sin(45)\]

Answer 5

where did you ge that formula