Which statement about the identity is correct?

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

Problem

Which statement about the identity

\sin^{2}\theta + \cos^{2}\theta = 1

is correct? (a) It holds only for

0^{\circ}\le \theta \le 90^{\circ}

. (b) It is true only when

\theta

is measured in degrees and not in radians. (c) It is true for all real values of

\theta

. (d) It fails when

\theta

is an odd multiple of

90^{\circ}