Question

evaluate
cos 75°+cos 15°​

Answer 1

We know that:

cosx + cosy = 2cos(x+y)/2 * cos(x-y)/2

Then :

cos75+cos15= 2 cos(75+15)/2 * cos(75-15)/2

= 2cos(90/2) * cos(60/2)

= 2cos(45)*cos(30)

= 2(sqrt2)/2) * sqrt(3)/2

= sqrt(6) /2

Answer 2

I Am Really Sorry :'(

cos75 + cos15 = ?

We know that:

cosx + cosy = 2cos(x+y)/2 * cos(x-y)/2

Then :

cos75+cos15= 2 cos(75+15)/2 * cos(75-15)/2

= 2cos(90/2) * cos(60/2)

= 2cos(45)*cos(30)

= 2(sqrt2)/2) * sqrt(3)/2

= sqrt(6) /2