Hassan khan's answer to Clara's Secondary 4 A Maths Singapore question.
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I hope this solution helpsssss!!!
Date Posted:
1 year ago
The line after 81 - 4k2 < 0 seems to be a step in the wrong direction.
4k2 > 81 is still not incorrect, but the following step is incorrect.
Correct is
4k2 - 81 > 0
(2k + 9) (2k - 9) > 0
k < -4.5 or k > 4.5
We take the case k < -4.5 as the coefficient of x2 must be negative for an expression to always be negative. Then, the largest corresponding possible value of k is -5.
4k2 > 81 is still not incorrect, but the following step is incorrect.
Correct is
4k2 - 81 > 0
(2k + 9) (2k - 9) > 0
k < -4.5 or k > 4.5
We take the case k < -4.5 as the coefficient of x2 must be negative for an expression to always be negative. Then, the largest corresponding possible value of k is -5.
Thanks for the amendments
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