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

Butterfly16 Group Title

Find an exact value. cos 15° Options: A) sqrt 6 + sqrt 2 / 4 B) - sqrt2 + sqrt 6 / 4 C) - sqrt2 - sqrt 6 / 4 D) - sqrt6 + 1 / 4

  • one year ago
  • one year ago

  • This Question is Closed
  1. Butterfly16 Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    A) \[ \frac{ \sqrt{6}+\sqrt{2} }{ 4 } \] B) \[\frac{ -\sqrt{2} +\sqrt{6} }{ 4 }\] C) \[\frac{ -\sqrt{2} - \sqrt{6} }{ 4 }\] D) \[\frac{ -\sqrt{6} +1}{ 4 }\]

    • one year ago
  2. amoodarya Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    cos(a-b)=cosa cosb + sina sin b you know? if ok cos (45-30)= cos45 cos 30 +sin 45 sin 30

    • one year ago
  3. Butterfly16 Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    where did you get all the numebrs?

    • one year ago
  4. amoodarya Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    |dw:1357845575004:dw| I dont get what you mean !

    • one year ago
  5. Butterfly16 Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    But its for cos 15° ?

    • one year ago
  6. amoodarya Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    It is an unknown angle you have to make it bu known angle

    • one year ago
  7. amoodarya Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    you know that formula? if yeah put the numbers in it you will have answer (a)

    • one year ago
  8. Butterfly16 Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    I think I got it. Can you help with another?

    • one year ago
  9. klimenkov Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    Also, you can use \(\cos^2\frac x 2=\frac{1+\cos x}2\).

    • one year ago
  10. Butterfly16 Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    @klimenkov Can you help with this one, pelase? Write the expression as either the sine, cosine, or tangent of a single angle. \[\cos(\frac{ \pi }{ 5 }) \cos(\frac{ \pi }{ 7 }) + \sin (\frac{ \pi }{ 5}) \sin (\frac{ \pi }{ 7 })\]

    • one year ago
  11. amoodarya Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    as "klimenkov " says you can use that formula shuch the way i draw|dw:1357846727839:dw|

    • one year ago
  12. amoodarya Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    cos(π/5)cos(π/7)+sin(π/5)sin(π/7)=cos (π/5-π/7) by the formula AS i sayd before cos (a+b)= cos a cos b-sin a sin b

    • one year ago
  13. Butterfly16 Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    so would the cos (a+b) be pi/5+pi/7?

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

    No. It will be \(\cos(\frac\pi5-\frac\pi7)\) as @amoodarya said. Hope you can do this subtraction.

    • one year ago
  15. amoodarya Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    no i think that you get it cos (a+b)= cos a cos b-sin a sin b cos (a-b)= cos a cos b+sin a sin b but 2pi/35 is unknown angle

    • one year ago
  16. Butterfly16 Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    \[\cos(\frac{ \pi }{ 5 }+\frac{ \pi }{ 7 })\] is 2pi/35? Can you show me how to fill in the formula? I think it'd make it easier for me.

    • one year ago
  17. amoodarya Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    cos (a-b)= cos a cos b+sin a sin b a=pi/5 b=pi/7

    • one year ago
  18. Butterfly16 Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    cos (pi/5-pi/7)= cos (pi/5) cos (pi/7)+sin (pi/5) sin (pi/7) ?

    • one year ago
  19. klimenkov Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    Yes.

    • one year ago
  20. Butterfly16 Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    So the answers 2pi/35?

    • one year ago
  21. klimenkov Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    No. The answer is \(\cos(\frac{2\pi}{35})\).

    • one year ago
  22. Butterfly16 Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    over 25?

    • one year ago
  23. klimenkov Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    No. Zoom in.

    • one year ago
  24. Butterfly16 Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    That's what I said?

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

    You said this without cosine.

    • 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.