The graph of quadratic function f (x) = AX2 + BX + C (a > B > C) has two different intersections A and B with X axis, and f (1) = 0. ① find the range of C / A; ② prove that 3 / 2 < ab <
(1) ∵f(1)=0
∴a+b+c=0
∴b=-a-c
Substituting a > b > C to get
a> - a-c > C (easy to get a > 0)
Reduced to - 2
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