Prove that 3(x+1)(x+7)-(2x+5)^2 is never positive?
回答 (4)
2018-10-19 1:31 am
If 2-2=0;2-2=0 again;
then -(0) is never positive.
cf:--(x-2)^=y ;
cf: -i^2 = -1.
then -(0) is never positive.
cf:--(x-2)^=y ;
cf: -i^2 = -1.
2018-10-21 9:50 am
3(x + 1)(x + 7) - (2x + 5)^2
= 3x^2 + 24x + 21 - 4x^2 - 20x - 25
= -x^2 + 4x - 4
= -(x - 2)^2
= 3x^2 + 24x + 21 - 4x^2 - 20x - 25
= -x^2 + 4x - 4
= -(x - 2)^2
2018-10-19 1:36 am
y = -(x - 2)^2
2018-10-19 1:30 am
If x - 2 is imaginary (i.e. any real number times i where i^2 = -1), then 3(x+1)(x+7)-(2x+5)^2 is positive.
For example, if x = 2 + i, then 3(x+1)(x+7)-(2x+5)^2 = 1
For example, if x = 2 + i, then 3(x+1)(x+7)-(2x+5)^2 = 1
收錄日期: 2021-05-01 00:24:08
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