Which one of the following expressions is equal to for every real value of ?

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

Problem

Which one of the following expressions is equal to

1

for every real value of

x

? (a)

(\sin x+\cos x)^2

(b)

\tan^{2}x+1

(c)

\sin^{2}x+\cos^{2}x

(d)

\sin x+\cos x