Got Homework?
Connect with other students for help. It's a free community.
Here's the question you clicked on:
 0 viewing
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
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

Butterfly16Best ResponseYou've already chosen the best response.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

amoodaryaBest ResponseYou've already chosen the best response.2
cos(ab)=cosa cosb + sina sin b you know? if ok cos (4530)= cos45 cos 30 +sin 45 sin 30
 one year ago

Butterfly16Best ResponseYou've already chosen the best response.0
where did you get all the numebrs?
 one year ago

amoodaryaBest ResponseYou've already chosen the best response.2
dw:1357845575004:dw I dont get what you mean !
 one year ago

Butterfly16Best ResponseYou've already chosen the best response.0
But its for cos 15° ?
 one year ago

amoodaryaBest ResponseYou've already chosen the best response.2
It is an unknown angle you have to make it bu known angle
 one year ago

amoodaryaBest ResponseYou've already chosen the best response.2
you know that formula? if yeah put the numbers in it you will have answer (a)
 one year ago

Butterfly16Best ResponseYou've already chosen the best response.0
I think I got it. Can you help with another?
 one year ago

klimenkovBest ResponseYou've already chosen the best response.0
Also, you can use \(\cos^2\frac x 2=\frac{1+\cos x}2\).
 one year ago

Butterfly16Best ResponseYou've already chosen the best response.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

amoodaryaBest ResponseYou've already chosen the best response.2
as "klimenkov " says you can use that formula shuch the way i drawdw:1357846727839:dw
 one year ago

amoodaryaBest ResponseYou've already chosen the best response.2
cos(π/5)cos(π/7)+sin(π/5)sin(π/7)=cos (π/5π/7) by the formula AS i sayd before cos (a+b)= cos a cos bsin a sin b
 one year ago

Butterfly16Best ResponseYou've already chosen the best response.0
so would the cos (a+b) be pi/5+pi/7?
 one year ago

klimenkovBest ResponseYou've already chosen the best response.0
No. It will be \(\cos(\frac\pi5\frac\pi7)\) as @amoodarya said. Hope you can do this subtraction.
 one year ago

amoodaryaBest ResponseYou've already chosen the best response.2
no i think that you get it cos (a+b)= cos a cos bsin a sin b cos (ab)= cos a cos b+sin a sin b but 2pi/35 is unknown angle
 one year ago

Butterfly16Best ResponseYou've already chosen the best response.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

amoodaryaBest ResponseYou've already chosen the best response.2
cos (ab)= cos a cos b+sin a sin b a=pi/5 b=pi/7
 one year ago

Butterfly16Best ResponseYou've already chosen the best response.0
cos (pi/5pi/7)= cos (pi/5) cos (pi/7)+sin (pi/5) sin (pi/7) ?
 one year ago

Butterfly16Best ResponseYou've already chosen the best response.0
So the answers 2pi/35?
 one year ago

klimenkovBest ResponseYou've already chosen the best response.0
No. The answer is \(\cos(\frac{2\pi}{35})\).
 one year ago

Butterfly16Best ResponseYou've already chosen the best response.0
That's what I said?
 one year ago

klimenkovBest ResponseYou've already chosen the best response.0
You said this without cosine.
 one year ago
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
 Engagement 19 Mad Hatter
 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.