Which of the following expressions is identically equal to for all real ?

MATHEMATICS · Single correct · A Level · Mathematics · Trigonometry · Trigonometry

Problem

Which of the following expressions is identically equal to cos⁡x\cos x for all real xx? (a) sin⁡(x−π2)\sin\left(x-\dfrac{\pi}{2}\right) (b) cos⁡(x−π2)\cos\left(x-\dfrac{\pi}{2}\right) (c) sin⁡(x+π2)\sin\left(x+\dfrac{\pi}{2}\right) (d) −sin⁡(x+π2)-\sin\left(x+\dfrac{\pi}{2}\right)

Related theory

Browse the problem library