Yahoo Answers is shutting down on May 4th, 2021 (Eastern Time) and beginning April 20th, 2021 (Eastern Time) the Yahoo Answers website will be in read-only mode. There will be no changes to other Yahoo properties or services, or your Yahoo account. You can find more information about the Yahoo Answers shutdown and how to download your data on this help page.
Trending News
Promoted
Can you help me with this trig. problem?
Use the power-reducing identity to find the exact value of cos2 (105°)
1 Answer
Relevance
- ☮ VašekLv 51 decade agoFavorite Answer
cos^2 x = (1 + cos 2x)/2
cos^2(105°) = (1 + cos(210°))/2 = (1 - cos(30°))/2 = (1 - sqrt(3)/2)/2 = 1/2 - sqrt(3)/4.
I used at one moment that shifting the argument of cos by 180° only changes the sign.
Hope this helps!
Still have questions? Get your answers by asking now.