lesterine's answer to .....'s Secondary 3 A Maths Singapore question.
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hope this helps
Date Posted:
2 years ago
Is it okay if I do it this way?
-x²+4x-7 = -(x-2)²-3
x² more than/equal to 0
-(x-2)² less than/equal to 0
-(x-2)²-3 than/equal to 0, therefore x²+4x-7 is always negative.
-x²+4x-7 = -(x-2)²-3
x² more than/equal to 0
-(x-2)² less than/equal to 0
-(x-2)²-3 than/equal to 0, therefore x²+4x-7 is always negative.
if you notice you have said that the perfect square you have constructed is less than OR equal to 0, which 0 is neither positive nor negative. since they want you to show it is ALWAYS negative, you cannot do this method.
It’s actually perfectly ok, with one slight improvement.
-(x - 2)^2 less than or equal to 0
-(x - 2)^2 - 3 less than or equal to -3
Means, -(x - 2)^2 - 3 is less than 0, or negative.
-(x - 2)^2 less than or equal to 0
-(x - 2)^2 - 3 less than or equal to -3
Means, -(x - 2)^2 - 3 is less than 0, or negative.
Ok! Thank you so much for your contributions!
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