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lilsis76
 3 years ago
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
lilsis76
 3 years ago
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

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

lilsis76
 3 years ago
Best ResponseYou've already chosen the best response.0YAY! 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?

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

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

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

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

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

lilsis76
 3 years ago
Best ResponseYou've already chosen the best response.0Cos(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 ???

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

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

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

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

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

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

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

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

lilsis76
 3 years ago
Best ResponseYou've already chosen the best response.0the points? is that what the ??? is for?

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

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

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