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# Is it really invertible?

Is $$\cos x = \dfrac1{\sec x}$$ and $$\sec x =\dfrac1{\cos x}$$ true (individually) for all $$x$$?

1 year, 3 months ago

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The above equalities are always true as they're identities, however, they are meaningful only when $$x ≠ (2n+1)\frac{\pi}{2}\,\,\forall\,\,n\,\epsilon\,\mathbb{Z}$$. · 1 year, 2 months ago