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phi Group TitleBest ResponseYou've already chosen the best response.1
do you know cos(x+y) formula?
 one year ago

Pianoman1996j Group TitleBest ResponseYou've already chosen the best response.1
Yes cosxcosy+sinxsiny
 one year ago

phi Group TitleBest ResponseYou've already chosen the best response.1
almost, the add turns into a minus (it's ugly that way) if you use that with y= x cos(x+x)= cos^2 x  sin^2 x replace sin^2 with 1cos^2 : cos^2  1  cos^2 or 2cos^2(x) 1
 one year ago

phi Group TitleBest ResponseYou've already chosen the best response.1
you can replace the cos(2x) with 2 cos^2(x) 1 if you call cos(x) y you have 2y^2 1 = y+2 solve for y
 one year ago

phi Group TitleBest ResponseYou've already chosen the best response.1
does that make sense?
 one year ago

Pianoman1996j Group TitleBest ResponseYou've already chosen the best response.1
I think. I will spend some time with it now. Thanks.
 one year ago

phi Group TitleBest ResponseYou've already chosen the best response.1
of course, after you find y, you find x using x = inverse cos(y) because this is a quadratic, you will get two answers for y then we have to figure out the the answers for every 2pi
 one year ago

phi Group TitleBest ResponseYou've already chosen the best response.1
*typo replace sin^2 with 1cos^2 : cos^2  (1  cos^2)= cos^2 1 + cos^2 or 2cos^2(x) 1
 one year ago

Pianoman1996j Group TitleBest ResponseYou've already chosen the best response.1
I think I have it! Hang on while I try to finish!!
 one year ago

Pianoman1996j Group TitleBest ResponseYou've already chosen the best response.1
I got y=3/2 and y=1. So 1 is at pi but what about 3/2. My teacher says pi is the only answer? Why?
 one year ago

phi Group TitleBest ResponseYou've already chosen the best response.1
the cosine goes between 1 and +1 (it never goes outside that range) . There is no angle whose cos is > 1 so you can't get 3/2
 one year ago

Pianoman1996j Group TitleBest ResponseYou've already chosen the best response.1
Of course! Thanks for helping me see.
 one year ago

phi Group TitleBest ResponseYou've already chosen the best response.1
and because the cosine repeats, you can add any multiple of 2pi to your answer and it will work. to be complete the answer is \[ \pi + 2\pi n \]where n is any integer
 one year ago

Pianoman1996j Group TitleBest ResponseYou've already chosen the best response.1
Is there any trick to knowing which formula to try? I often grab one that would be allowed but isn't the one I should have used.
 one year ago

Pianoman1996j Group TitleBest ResponseYou've already chosen the best response.1
I only had to give solutions between 0 and 2pi but I like your further explaination
 one year ago

Pianoman1996j Group TitleBest ResponseYou've already chosen the best response.1
Oops. Explanation I mean
 one year ago

phi Group TitleBest ResponseYou've already chosen the best response.1
Unfortunately, with trig I think you just have to do a bunch of problems and build a sense of what might work.
 one year ago

Pianoman1996j Group TitleBest ResponseYou've already chosen the best response.1
Lol. I've done hundreds and am still picking the wrong ones. But I'm not giving up yet!
 one year ago

Pianoman1996j Group TitleBest ResponseYou've already chosen the best response.1
Thanks for help. my midterm is soon. Yikes.
 one year ago
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