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sin(2pi/7)/(1+cos(2pi/7)) can someone show me how to manipulate this

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).

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