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lilsis76
Group Title
using addition formulas for sine and cosine to simplify the expression:
cos (2pi/9) cos (pi/18) + sin (2pi/9) sin(pi/18)
I want to learn it the normal way first before I add my instructors instructions to place S=45 & T = 30.
here are the formulas given:
sin(s+t) = sin s cos t + cos s sine t
sin(st) = sin s cos t  cos s sine t
cos(s+t) = cos s cos t  sin s sin t
cos(st) = cos s cos t + sin s sin t
The they way it looks, it seems to use formula 4:
cos(st) = cos s cos t + sin s sin t
 2 years ago
 2 years ago
lilsis76 Group Title
using addition formulas for sine and cosine to simplify the expression: cos (2pi/9) cos (pi/18) + sin (2pi/9) sin(pi/18) I want to learn it the normal way first before I add my instructors instructions to place S=45 & T = 30. here are the formulas given: sin(s+t) = sin s cos t + cos s sine t sin(st) = sin s cos t  cos s sine t cos(s+t) = cos s cos t  sin s sin t cos(st) = cos s cos t + sin s sin t The they way it looks, it seems to use formula 4: cos(st) = cos s cos t + sin s sin t
 2 years ago
 2 years ago

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dpaInc Group TitleBest ResponseYou've already chosen the best response.1
yes.... it is that 4th formula..
 2 years ago

lilsis76 Group TitleBest ResponseYou've already chosen the best response.0
YAY! okay um... i know that know would i fill it in like this... well wait, first I have a question, how can i find out if its cos or sin that im looking for?
 2 years ago

lilsis76 Group TitleBest ResponseYou've already chosen the best response.0
wait it would be the cos. right? ugh these formulas are confusing me
 2 years ago

dpaInc Group TitleBest ResponseYou've already chosen the best response.1
yes... the cosine one... just remember, the cosine formula (whether it's + or ), is cos * cos +/ sin * sin
 2 years ago

lilsis76 Group TitleBest ResponseYou've already chosen the best response.0
okay, ill have to put that on a 3by5 card
 2 years ago

lilsis76 Group TitleBest ResponseYou've already chosen the best response.0
okay! i think i got this just a second. let me know if its right or i made a mistake please.
 2 years ago

dpaInc Group TitleBest ResponseYou've already chosen the best response.1
so: \(\large cos(\frac{2\pi}{9}\frac{\pi}{18})=cos(\frac{2\pi}{9})cos(\frac{\pi}{18})+sin(\frac{2\pi}{9})sin(\frac{\pi}{18}) \)
 2 years ago

lilsis76 Group TitleBest ResponseYou've already chosen the best response.0
Cos(2pi/9 – pi/18) mult. 2 to the left side……. So cos(4pi/18pi/18) I guess giving me…….cos 3pi/18? Or do I simplify to get the cos pi/6 ???
 2 years ago

dpaInc Group TitleBest ResponseYou've already chosen the best response.1
now... \(\large \frac{2\pi}{9}\frac{\pi}{18}=\frac{4\pi}{18}\frac{\pi}{18}=\frac{3\pi}{18}=\frac{\pi}{6} \) that expression actually is cos(pi/6)
 2 years ago

dpaInc Group TitleBest ResponseYou've already chosen the best response.1
are you familiar with the unit circle?
 2 years ago

lilsis76 Group TitleBest ResponseYou've already chosen the best response.0
yes, i had to memorize that thingy
 2 years ago

dpaInc Group TitleBest ResponseYou've already chosen the best response.1
wow... you seem like you don't need any help.... :)
 2 years ago

lilsis76 Group TitleBest ResponseYou've already chosen the best response.0
so...my answer is going to be that unit?
 2 years ago

lilsis76 Group TitleBest ResponseYou've already chosen the best response.0
ugh?! i do need h
 2 years ago

dpaInc Group TitleBest ResponseYou've already chosen the best response.1
so what's cos(pi/6) = ???
 2 years ago

lilsis76 Group TitleBest ResponseYou've already chosen the best response.0
haha sorry about that. i just need help of steps walking through it, she went so fast in class. i only got pieces
 2 years ago

dpaInc Group TitleBest ResponseYou've already chosen the best response.1
yes... cos(pi/6) = cos(30 degrees) = ????
 2 years ago

lilsis76 Group TitleBest ResponseYou've already chosen the best response.0
the points? is that what the ??? is for?
 2 years ago

dpaInc Group TitleBest ResponseYou've already chosen the best response.1
yes.... what's the xcoordinate ??? here is the unit circle...page 3 http://tutorial.math.lamar.edu/pdf/Trig_Cheat_Sheet.pdf
 2 years ago

lilsis76 Group TitleBest ResponseYou've already chosen the best response.0
\[\sqrt{3}/2 , 1/2\]
 2 years ago

dpaInc Group TitleBest ResponseYou've already chosen the best response.1
i have to leave... sorry... the answer is cos(30 degrees) = \(\large \frac{\sqrt3}{2} \)
 2 years ago

lilsis76 Group TitleBest ResponseYou've already chosen the best response.0
okay, thank u, bye!
 2 years ago

dpaInc Group TitleBest ResponseYou've already chosen the best response.1
the xcoordinate refers to the cosine, the ycoordinate is sine. yw... :)
 2 years ago
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