Answer is sin18° = (√5-1)/4 Let A=18° 3A+2A=90° sin(3A)=-sin(90-2A) 3sinA-4sin^3(A)= cos2A = 1-sin^2(A) 4sin^3(A)-2sin^2(A)-3sinA+1=0 (SinA-1) ...
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