Quantcast

Got Homework?

Connect with other students for help. It's a free community.

  • across
    MIT Grad Student
    Online now
  • laura*
    Helped 1,000 students
    Online now
  • Hero
    College Math Guru
    Online now

Here's the question you clicked on:

55 members online
  • 0 replying
  • 0 viewing

aussy123

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

  • one year ago
  • one year ago

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

    you don't need the sine part

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

    then how do I start

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

    Two variables?

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

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

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

    |dw:1364529999084:dw|

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

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

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

    costheta= -4/5 I need cosx

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

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

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

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

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

    When I do it I get 169

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

    a denominator of 169

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

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

    • one year ago
  13. tomhoffhim
    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

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

    yea I had to put theta for that

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

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

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

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

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

    there is your 169

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

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

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

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

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

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

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

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

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

    I know but that is what is already given

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

    oh damn i made a mistake!! sorry

    • one year ago
  24. tomhoffhim
    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

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

    lol its okay, Ive made plenty

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

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

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

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

    • one year ago
  28. aussy123
    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

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

    nvm. I found the formula, Thank you!

    • one year ago
    • Attachments:

See more questions >>>

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.