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

This Question is Closed

zepdrixBest ResponseYou've already chosen the best response.1
Hmmmmm 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.
 one year ago

lilsis76Best ResponseYou've already chosen the best response.0
well... okay we have the 30 and 45 angles
 one year ago

zepdrixBest ResponseYou've already chosen the best response.1
Hmm 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
 one year ago

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

lilsis76Best ResponseYou've already chosen the best response.0
the 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??
 one year ago

zepdrixBest ResponseYou've already chosen the best response.1
Mmmmmmmmmmmmmm yah looks good. Now it's special angle time! :OOO
 one year ago

zepdrixBest ResponseYou've already chosen the best response.1
Let'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
 one year ago

lilsis76Best ResponseYou've already chosen the best response.0
OH....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
 one year ago

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

lilsis76Best ResponseYou've already chosen the best response.0
what?! the 30 ? um... hold on
 one year ago

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

lilsis76Best ResponseYou've already chosen the best response.0
okay tis.. (sqrt2 /2)( sqrt3/2)  (sqrt 2/2)(1/2)
 one year ago

zepdrixBest ResponseYou've already chosen the best response.1
k good good c: Now simplyyyyyyyyyy \:D/
 one year ago

lilsis76Best ResponseYou've already chosen the best response.0
uh...hold on let me try doin it um..
 one year ago

zepdrixBest ResponseYou've already chosen the best response.1
dw:1350602295589:dw Hmmmm this is what I'm coming up with D:
 one year ago

lilsis76Best ResponseYou've already chosen the best response.0
okay, but wouldn't it be  sqrt 4 /2?
 one year ago

zepdrixBest ResponseYou've already chosen the best response.1
Water you talking about? D:
 one year ago

lilsis76Best ResponseYou've already chosen the best response.0
like okay, wouldnt the sqrt 6 / 4  sqrt2/4 be a sqrt 4/4 leading to 2/4=1/2 ?
 one year ago

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

lilsis76Best ResponseYou've already chosen the best response.0
okay, so next time i get sq roots like that, just leave it alone?
 one year ago

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

lilsis76Best ResponseYou've already chosen the best response.0
okay then, thank you for helping me :D
 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.