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curious phenomenon.
Quadratic formula
Quartic formula - Ferrari's method of
solving a quartic equation
Trig
Functions of Special Angles, part 2 -- in this page, we look at a fun
problem involving cos 40�, cos 80�, and cos 160�. It turns out these
three cosines are the roots of 8x³-6x+1=0. Since these three roots
are all real, the cubic formula doesn't work without complex numbers, but it
does work, and it finds all three roots.