SOLUTION: Can you help with equation; calculate exact value ; cos 105 degrees

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Question 978087: Can you help with equation; calculate exact value ; cos 105 degrees
Found 2 solutions by MathLover1, Alan3354:
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!

Use the formula,

cos+%2890+%2B+15%29+=+%28cos+%2890%29%2Acos+%2815%29%29+-+%28sin+%2890%29%2Asin+%2815%29%29
Since cos%28+90%29+=+0 and sin+%2890%29+=+1, we have
cos+%2890+%2B+15%29+=+%280+%2A+cos+%2815%29%29+-+%281+%2A+sin+%2815%29%29
cos+%2890+%2B+15%29+=+-sin%28+15%29

-sin+%2815%29=++-%28sqrt%283%29-1%29%2F%282%2Asqrt%282%29%29 or %281-sqrt%283%29%29%2F%282%2Asqrt%282%29%29


Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
That's not an equation.
Equations have equal signs.