cos ( − 1 ∘ ) + cos ( − 2 ∘ ) + cos ( − 3 ∘ ) + ⋯ + cos ( − 8 9 ∘ ) − sin ( − 1 ∘ ) − sin ( − 2 ∘ ) − sin ( − 3 ∘ ) − ⋯ − sin ( − 8 9 ∘ ) = ?
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This is the same as Summation of sin x from 1 to 89 all over summation of cos x from 1 to 89 degrees. Take note that by co-function, sin 1 = cos 89. Thus the numerator is the same as denominstor Therefore, the answer is 1.
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Q = cos ( − 1 ∘ ) + cos ( − 2 ∘ ) + cos ( − 3 ∘ ) + ⋯ + cos ( − 8 9 ∘ ) − sin ( − 1 ∘ ) − sin ( − 2 ∘ ) − sin ( − 3 ∘ ) − ⋯ − sin ( − 8 9 ∘ ) = cos ( 1 ∘ ) + cos ( 2 ∘ ) + cos ( 3 ∘ ) + ⋯ + cos ( 8 9 ∘ ) sin ( 1 ∘ ) + sin ( 2 ∘ ) + sin ( 3 ∘ ) + ⋯ + sin ( 8 9 ∘ ) = sin ( 8 9 ∘ ) + sin ( 8 8 ∘ ) + sin ( 8 7 ∘ ) + ⋯ + sin ( 1 ∘ ) sin ( 1 ∘ ) + sin ( 2 ∘ ) + sin ( 3 ∘ ) + ⋯ + sin ( 8 9 ∘ ) = 1 Note that sin ( − θ ) = − sin θ , cos ( − θ ) = cos θ Note that cos ( 9 0 ∘ − θ ) = sin θ