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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
 one year ago
 one year 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
 one year ago
 one year ago

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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