How do you find the exact value of $cos(theta) = -1$ ?

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Answer 1 · 2018-05-04T11:15:41

We don't really find it so much as just know it's $theta = 180^circ + 360^circ k quad$ for integer $k$ .

How do we really know $cos 180^circ = -1$ ? Perhaps the supplementary angle formula:

$cos(180^circ - theta) = - cos theta$

$cos(180^circ - 0^circ) = -cos 0^circ = -1 quad sqrt$

How do you find the exact value of cos(theta) = -1cos(theta) = -1?