constructible angles-->help please 1. The problem statement, all variables and given/known data x=2(pi)/7 we will show that this is not constructible and therefore 7-gon is not constructible. a) show cos4x = cos3x b) Use the above equation to find a rational quartic polynomial f(y) where f(cos x) = 0. c)From f, find a cubic rational polynomial g(y) where g(cos x) = 0 2. Relevant equations see above 3. The attempt at a solution im having trouble in part b). i expanded cos4x - cos3x = 0 in terms of cos(x) and I made the substitution y= cos(x) i got the quartic equation 8y^4 + 4y^3 - 8y^(2) -3y + 1 =0. but when i put y= cos(2(pi)/7)) it dosent come out to 0.