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Find the fourth root of the equation

Source:

October 7, 2010
trigonometryfunctionalgebra proposedalgebra

Problem Statement

Three of the roots of the equation x4px3+qx2rx+s=0x^4 -px^3 +qx^2 -rx+s = 0 are tanA,tanB\tan A, \tan B, and tanC\tan C, where A,BA, B, and CC are angles of a triangle. Determine the fourth root as a function only of p,q,rp, q, r, and s.s.