The sides of a triangle are in AP

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

Problem

The sides of a triangle are in AP. If the angles

A

and

C

are the greatest and smallest angles, respectively, then

4(1-\cos A)(1-\cos C)

is equal to (1)

\cos A-\cos C

(2)

\cos A\cos C

(3)

\cos A+\cos C

(4)

\cos C-\cos A