Multiple choice general knowledge

cos(x+y)=

  1. cosx cosy+sinx siny

  2. cosx siny-sinx cosy

  3. cosx cosy - sinx siny

  4. sinx siny + cosx cosy

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The cosine addition formula is cos(x+y) = cos x cos y - sin x sin y. This is a fundamental trigonometric identity for expanding cosine of a sum. Option A has the wrong sign, B mixes sine and cosine incorrectly, and D just reorders the terms but still has the wrong sign.