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What is the simplified value of \(\cos(\pi+x)+\cos(\pi-x)\)?

Answer and explanation

Correct answer: \(-2\cos x\)

Using allied-angle identities, \(\cos(\pi+x)=-\cos x\) and \(\cos(\pi-x)=-\cos x\). Hence, \(\cos(\pi+x)+\cos(\pi-x)=-\cos x-\cos x=-2\cos x\). The value \(0\) may occur only for particular values such as when \(\cos x=0\); it is not the general simplified form. Exam tip: For angles of the form \(\pi\pm x\), first check the sign of the trigonometric function.

Related tags

Trigonometric FunctionsAllied AnglesCosine IdentitiesTrigonometric SimplificationClass 11Trigonometric Functions And Their PropertiesMathematicsClass 12 Mcq

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