# Prove if y=arcsin x has the range -pi/2 .....pi/2 implies that cos x >/= 0?

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- 4 weeks ago
it s obvious but it is about derivative: y'= 1/1-x^2, book says : ignore negative sign because cos x is always positive (-pi/2....pi/2)

- Keith ALv 64 weeks ago
(Ted S's answer ducks the issue, and thus is correct; but) it should be cos y ≥ 0 .

- ted sLv 74 weeks ago
comment ; a domain of [ - π / 2 , π / 2 ] has cosine ≥ 0.......alt242 for ≥ symbol

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