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Find the value of \(\cos^{-1}\left(\frac{4}{5}\right)+\sin^{-1}\left(\frac{4}{5}\right)\).

Answer and explanation

Correct answer: \(\frac{\pi}{2}\)

Use the identity \(\sin^{-1}x+\cos^{-1}x=\dfrac{\pi}{2}\) valid for \(x\in[-1,1]\). Here \(x=4/5\) lies in the domain, so the sum equals \(\dfrac{\pi}{2}\). Why other options fail: \(\frac{\pi}{6}\) (30°) is not the complement of the corresponding angles here, and \(\frac{3\pi}{2}\) or 0 are clearly inconsistent with principal values of arcsin/arccos. Exam tip: memorize the complementary identity and always check the domain before applying it.

Related tags

Inverse Trigonometric FunctionsArcsin ArccosTrigonometric IdentitiesClass 12EasyProperties Of Inverse Trigonometric FunctionsMathematicsClass 12 Mcq

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