Condition for a Double Root of a Quadratic
Source:
June 13, 2009
quadraticsVietaalgebraquadratic formula
Problem Statement
For one root of ax^2 \plus{} bx \plus{} c \equal{} 0 to be double the other, the coefficients must be related as follows:
(A)\ 4b^2 \equal{} 9c\qquad
(B)\ 2b^2 \equal{} 9ac\qquad
(C)\ 2b^2 \equal{} 9a\qquad \\
(D)\ b^2 \minus{} 8ac \equal{} 0\qquad
(E)\ 9b^2 \equal{} 2ac