Ryan Patel's answer to Jona's Secondary 4 A Maths Singapore question.
Not sufficient. Try drawing y = -x^2 + 6x - 2.
Correct is this.
Condition 1: a < 0
Condition 2: Discriminant < 0
36 - 4ac < 0
ac > 9
a must be negative AND the product ac must exceed 9.
We just have to find two negative values which multiply to become a giant number, like -2 and -10.
Correct is this.
Condition 1: a < 0
Condition 2: Discriminant < 0
36 - 4ac < 0
ac > 9
a must be negative AND the product ac must exceed 9.
We just have to find two negative values which multiply to become a giant number, like -2 and -10.
In your case, the two forms in (i) and (ii) which you have listed are not exactly equivalent (i.e. the "c" in both cases do not represent the same expression).
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