A community for students.
Here's the question you clicked on:
 0 viewing
lilsis76
 2 years ago
Use the formula cos(s+t)=cos s cos t  sin s sin t:
to compute the exact value of cos 75 degrees.
all i know is that 75 degrees is between 90 deg and 60 degrees on a unit circle.
lilsis76
 2 years ago
Use the formula cos(s+t)=cos s cos t  sin s sin t: to compute the exact value of cos 75 degrees. all i know is that 75 degrees is between 90 deg and 60 degrees on a unit circle.

This Question is Closed

zepdrix
 2 years ago
Best ResponseYou've already chosen the best response.1Hmmmmm we have special angles for 30, 45, 60, 90... do any of those 2 add up to 75? Cause that would really help us out in this problem.

lilsis76
 2 years ago
Best ResponseYou've already chosen the best response.0well... okay we have the 30 and 45 angles

zepdrix
 2 years ago
Best ResponseYou've already chosen the best response.1Hmm good good :) I think we can work with that. So we'll rewrite cos(75) as cos(45+30). After we apply the sum formula, we should be able to plug in a BUNCH of special angles and HOPEFULLY we'll be able to simplify it :3 hehe

zepdrix
 2 years ago
Best ResponseYou've already chosen the best response.1So use your formula you posted at the top, what will your setup look like? :D

lilsis76
 2 years ago
Best ResponseYou've already chosen the best response.0the 45 will be the s, and t will be tht 30 so... cos(s+t)=cos s cos t  sin s sin t: cos(45+30)= cos 45 cos 30  sin 45 sin 30. yes??

zepdrix
 2 years ago
Best ResponseYou've already chosen the best response.1Mmmmmmmmmmmmmm yah looks good. Now it's special angle time! :OOO

zepdrix
 2 years ago
Best ResponseYou've already chosen the best response.1Let's look at the first ..thing.. cos(45), what is the cosine of 45 degrees? It's a special angle that you're suppose to remember.. (from the unit circle) :X

lilsis76
 2 years ago
Best ResponseYou've already chosen the best response.0OH....so the points are the special angles??? I thought that meant another formula to remember. um... 45 is at squ rt. 2 / squ rt. 2 / 2 cos sin cos is squ.rt. 2 / 2

zepdrix
 2 years ago
Best ResponseYou've already chosen the best response.1so cos(45)=sqrt2/2 and cos(30)? :D Go through all of them and do yer magic!

lilsis76
 2 years ago
Best ResponseYou've already chosen the best response.0what?! the 30 ? um... hold on

zepdrix
 2 years ago
Best ResponseYou've already chosen the best response.1so our first term cos(45)cos(30) becomes.. (sqrt2/2)(sqrt3/2) Which we should be able to simplify a little bit. hmm

lilsis76
 2 years ago
Best ResponseYou've already chosen the best response.0okay tis.. (sqrt2 /2)( sqrt3/2)  (sqrt 2/2)(1/2)

zepdrix
 2 years ago
Best ResponseYou've already chosen the best response.1k good good c: Now simplyyyyyyyyyy \:D/

lilsis76
 2 years ago
Best ResponseYou've already chosen the best response.0uh...hold on let me try doin it um..

zepdrix
 2 years ago
Best ResponseYou've already chosen the best response.1dw:1350602295589:dw Hmmmm this is what I'm coming up with D:

lilsis76
 2 years ago
Best ResponseYou've already chosen the best response.0okay, but wouldn't it be  sqrt 4 /2?

zepdrix
 2 years ago
Best ResponseYou've already chosen the best response.1Water you talking about? D:

lilsis76
 2 years ago
Best ResponseYou've already chosen the best response.0like okay, wouldnt the sqrt 6 / 4  sqrt2/4 be a sqrt 4/4 leading to 2/4=1/2 ?

zepdrix
 2 years ago
Best ResponseYou've already chosen the best response.1No you can't subtract those sqrt's like that :c you have to leave them alone.

lilsis76
 2 years ago
Best ResponseYou've already chosen the best response.0okay, so next time i get sq roots like that, just leave it alone?

zepdrix
 2 years ago
Best ResponseYou've already chosen the best response.1Yah that is a good place to stop c: \[\frac{ \sqrt6 \sqrt2 }{ 4 }\]

lilsis76
 2 years ago
Best ResponseYou've already chosen the best response.0okay then, thank you for helping me :D
Ask your own question
Sign UpFind more explanations on OpenStudy
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.