What does $cos (arctan (1)) - 2 sin (arccos (9))$ $cos(arctan(1))-2sin(arccos(9))$ equal?

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Answer 1 · 2016-05-14T08:07:35

I am surprised to read questions on evaluation of invalid expressions, from different sources.

Let a = arc cos 9. Then, cos a = 9 > 1. so, the given expression is invalid.

For long-tern-memory, both cos x and sin x $\in [- 1, 1]$ $in [-1, 1]$ .

What does cos(arctan(1))−2sin(arccos(9))cos(arctan(1))-2sin(arccos(9)) equal?