Derivation of Weida formula?
Let ax ^ 2 + BX + C = 0 (a is not 0)
When △≥ 0
X1 = (- B + root △) / 2A x2 = (- B - root △) / 2A
So X1 + x2 = [(- B + radical △) / 2A] + [(- B - radical △) / 2A]
=-2b/2a
=-b/a
Similarly, x1x2 = [(- B + root △) / 2A] * [(- B - root △) / 2A]
=[(-b)^2-(b^2-4ac)]/4a^2
=4ac/4a^2
=c/a
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