If tan x=−1, and 90°<x<180°, what is cos⁡

Answer 1

INVTAN (-1) = -45 Degrees. But the problem states that x has to be in the second quadrant (90 <x< 180). Transferring the angler into the second quadrant: x = 180 + (- 45) = 135 Degrees. Check that the TAN of 135 is also -1. TAN (135) = -1.

So, the COS (135) = -0.7071.

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