Can x|x|^3 change into x^4?
回答 (2)
2017-09-25 1:53 pm
Only for x ≥ 0.
The sign of x|x|^3 is the same as the sign of x.
The sign of x^4 is never negative.
The sign of x|x|^3 is the same as the sign of x.
The sign of x^4 is never negative.
2017-09-25 10:23 pm
for x ≥ 0, it works:
x ≥ 0, x^3 ≥ 0 => x|x|^3 = x^4
for x < 0, |x|^3 = (-x)^3 => x|x|^3 = -x^4
x ≥ 0, x^3 ≥ 0 => x|x|^3 = x^4
for x < 0, |x|^3 = (-x)^3 => x|x|^3 = -x^4
收錄日期: 2021-04-23 22:02:52
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