A community for students.

Here's the question you clicked on:

55 members online
  • 0 replying
  • 0 viewing

anonymous

  • 5 years ago

use double angle formula to find the exact value of 2cos^2(3pie/8)-1

  • This Question is Closed
  1. anonymous
    • 5 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    Okay...

  2. anonymous
    • 5 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    Use the fact that\[\cos{2 \theta}=\cos^2 \theta -\sin^2 \theta=2\cos^2 \theta -1\]

  3. anonymous
    • 5 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    For\[\theta = \frac{3\pi}{8}\]\[\cos 2 \theta =\cos \frac{3 \pi}{4}=\cos^2 \frac{3 \pi}{8}-1\]The right-hand side is your expression. Now

  4. anonymous
    • 5 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    \[\frac{3\pi}{4}\] lies in the second quadrant where cosine is negative. 3pi/4 is equivalent to 135 degrees. The cosine of 135 degrees is equal to the the negative cosine of 45 degrees, which has an exact value of \[-\frac{1}{\sqrt{2}}\]

  5. anonymous
    • 5 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    thank you!!!

  6. anonymous
    • 5 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    become a fan! would love the points

  7. anonymous
    • 5 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    what is the exact value of 2sin 157.5 cos 157.5

  8. anonymous
    • 5 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    This is an example of double angle for sine.\[\sin 2 \theta = 2 \sin \theta \cos \theta\]Here theta is 157.5, so 2 x theta = 315 degrees. 315 = 360 - 45 This lies in the fourth quadrant where sine is negative. You have sin(315)=-sin(45)= -1/sqrt(2) again.

  9. anonymous
    • 5 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    it says write the following expression as sin cos or tan of a double agent. then find the exact value

  10. Not the answer you are looking for?
    Search for more explanations.

    • Attachments:

Ask your own question

Sign Up
Find more explanations on OpenStudy
Privacy Policy

Your question is ready. Sign up for free to start getting answers.

spraguer (Moderator)
5 → View Detailed Profile

is replying to Can someone tell me what button the professor is hitting...

23

  • Teamwork 19 Teammate
  • Problem Solving 19 Hero
  • You have blocked this person.
  • ✔ You're a fan Checking fan status...

Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.

This is the testimonial you wrote.
You haven't written a testimonial for Owlfred.