Homework Help

 Use the equation twice to find cos(15) if it known that cos(60)=0.5

user profile pic

creations | Student, Undergraduate | eNotes Newbie

Posted December 12, 2011 at 6:01 AM via web

dislike 0 like

 Use the equation twice to find cos(15) if it known that cos(60)=0.5

Tagged with engineering trig, math

1 Answer | Add Yours

user profile pic

sciencesolve | Teacher | (Level 3) Educator Emeritus

Posted December 12, 2011 at 4:43 PM (Answer #1)

dislike 0 like

You need to use the formula of half angle such that:

`cos (alpha/2) = sqrt ((1 +cos alpha)/2)`

You have recommended to use the cosine of the angle of `60^o` .

`cos 30^o = cos (60^o/2) = sqrt ((1 + cos 60^o)/2)`

`cos 30^o = cos (60^o/2) = sqrt ((1 + 0.5)/2)`

`cos 30^o = cos (60^o/2) = sqrt ((1.5)/2)`

`cos 15^o = cos (30^o/2) = sqrt ((1 + sqrt ((1.5)/2))/2)`

`cos 15^o~~`  0.965

The value of cos `15^o` `~~` 0.965.

Join to answer this question

Join a community of thousands of dedicated teachers and students.

Join eNotes