rinik Posted September 20, 2013 Report Share Posted September 20, 2013 the answer is tan(pi/7) Reply Link to post Share on other sites More sharing options...
flinquinnster Posted September 20, 2013 Report Share Posted September 20, 2013 So here you would use the double angle formulas. So sin(2A)=2sinAcosA and cos(2A) = 2(cosA)^2-1 - you want to use this form of cos(2A) as you want everything to cancel out in the denominator. So, when you simplify sin(2pi/7)/(1-cos(2pi/7), you get 2sin(pi/7)cos(pi/7)/2(cos(pi/7))^2 = sin(pi/7)/cos(pi/7) = tan(pi/7). 1 Reply Link to post Share on other sites More sharing options...
~Lc~ Posted September 20, 2013 Report Share Posted September 20, 2013 If you want a breakdown of the double angle forumlas, I found this while trying to solve the problem:http://mathworld.wolfram.com/Double-AngleFormulas.html Reply Link to post Share on other sites More sharing options...
rinik Posted September 20, 2013 Author Report Share Posted September 20, 2013 Thanks. I was revising and I didn't notice that I can use that Reply Link to post Share on other sites More sharing options...
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