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lilsis76
 3 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
 3 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.

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zepdrix
 3 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
 3 years ago
Best ResponseYou've already chosen the best response.0well... okay we have the 30 and 45 angles

zepdrix
 3 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
 3 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
 3 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
 3 years ago
Best ResponseYou've already chosen the best response.1Mmmmmmmmmmmmmm yah looks good. Now it's special angle time! :OOO

zepdrix
 3 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
 3 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
 3 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
 3 years ago
Best ResponseYou've already chosen the best response.0what?! the 30 ? um... hold on

zepdrix
 3 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
 3 years ago
Best ResponseYou've already chosen the best response.0okay tis.. (sqrt2 /2)( sqrt3/2)  (sqrt 2/2)(1/2)

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

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

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

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

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

lilsis76
 3 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
 3 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
 3 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
 3 years ago
Best ResponseYou've already chosen the best response.1Yah that is a good place to stop c: \[\frac{ \sqrt6 \sqrt2 }{ 4 }\]

lilsis76
 3 years ago
Best ResponseYou've already chosen the best response.0okay then, thank you for helping me :D
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