Quantcast

A community for students.

Here's the question you clicked on:

55 members online
  • 0 replying
  • 0 viewing

aussy123

  • 2 years ago

Given: costheta= -4/5, sin x =-12/13 ,theta is in the third quadrant, and x is in the fourth quadrant; evaluate cos 2x. -119/169 119/169 -11/13

  • This Question is Closed
  1. satellite73
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    you don't need the sine part

  2. aussy123
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    then how do I start

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

    Two variables?

  4. satellite73
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    \[\cos(2x)=2\cos^2(x)-1\]

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

    |dw:1364529999084:dw|

  6. satellite73
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    oh i see there is a \(\theta\) and an \(x\)

  7. aussy123
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    costheta= -4/5 I need cosx

  8. satellite73
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    you are asked for \(\cos(2x)\) where \(\sin(x)=-\frac{12}{13}\)

  9. satellite73
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    \[\cos(2x)=1-2\sin^2(x)\]

  10. aussy123
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    When I do it I get 169

  11. aussy123
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    a denominator of 169

  12. satellite73
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    there is no \(\theta \) in your question

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

    ok, I'll do it for you, give me a second, this is an easy question

  14. aussy123
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    yea I had to put theta for that

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

    satellite, you don't know what you're doing..

  16. satellite73
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    \[\cos(x)=1-2\sin^2(x)\] \[\cos(x)=1-(\frac{-12}{13})^2\]\

  17. satellite73
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    there is your 169

  18. satellite73
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    \[\cos(2x)=1-(\frac{12}{13})^2\] \[\cos(2x)=1-\frac{144}{169}\]

  19. satellite73
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    \[\cos(2x)=\frac{25}{169}\]

  20. aussy123
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    I know, thats what I get, but it isnt a choice

  21. satellite73
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    your question asks for \(\cos(2x)\) and doesn't mention any \(\theta\)

  22. aussy123
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    I know but that is what is already given

  23. satellite73
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    oh damn i made a mistake!! sorry

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

    I'm too lazy to do it but you need to draw the triangles and either use theta or x for the angle

  25. aussy123
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    lol its okay, Ive made plenty

  26. satellite73
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    \[\cos(2x)=1-2\sin^2(x)\] \[\cos(2x)=1-2\times (\frac{12}{13})^2\] \[cos(2x)=1-2\times \frac{144}{169}\]

  27. satellite73
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 1

    \[\cos(2x)=1-\frac{288}{169}\]\[\cos(2x)=-\frac{119}{169}\]

  28. aussy123
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    Lol this is a lot of work, can you use this same formula for tan2Theta

  29. aussy123
    • 2 years ago
    Best Response
    You've already chosen the best response.
    Medals 0

    nvm. I found the formula, Thank you!

  30. 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.