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A student claims that \(\sin(\pi-x)=-\sin x\). Which is the correct correction of the error?

Answer and explanation

Correct answer: \(\sin(\pi-x)=\sin x\), because sine is positive in the second quadrant.

Using the subtraction formula, \(\sin(\pi-x)=\sin\pi\cos x-\cos\pi\sin x=0-(-1)\sin x=\sin x\). The angle \(\pi-x\) is in quadrant II, where sine is positive. Exam tip: check the quadrant sign for identities involving \(\pi\pm x\).

Related tags

Trigonometric IdentitiesAllied AnglesSine FunctionQuadrant SignsClass 11 MathematicsTrigonometric Functions And Their PropertiesTrigonometric FunctionsMathematics

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