Question

Evaluate the following

cos 60° cos 45° - sin 60° ∙ sin 45°

Answer 1

cos 60° cos 45° - sin 60° ∙ sin 45° …(i)

By trigonometric ratios we know that,

`cos 60^@ = 1/2 cos 45^@ = 1/sqrt2`

`sin 60^@ = sqrt3/2    sin 45^@ = 1/sqrt2`

By substituting above value in (i), we get

`1/2. 1/sqrt2 - sqrt3/2. 1/sqrt2 => (1 - sqrt3)/(2sqrt2)`