6ax^(-7) - 12bx^(-13)
= 6x^(-13)(ax^6-2b)
因 6x^(-13) > 0, 而實數並無零因子, 也就是說:
若 pq = 0 則 p = 0 或 q = 0.
所以
6ax^(-7) - 12bx^(-13) = 0
if and only if ax^6 - 2b = 0
if and only if x^6 = 2b/a
又: x^m = r, 其中 m 是正整數, 則
(1) x = r^(1/m), 或
(2) m 是偶數, x = - r^(1/m).
所以:
x^6 = 2b/a if and only if x = ± (2b/a)^(1/6)
a > 0, b > 0, x > 0 則6ax^(-7) - 12bx^(-13) = 0 if and only if x^6 = 2b/a if and only if x = ± (2b/a)^(1/6)?
2020-10-24 1:31 pm
回答 (1)
2020-10-24 1:45 pm
✔ 最佳答案
懂了，謝謝~~~~~~~~~~~~
收錄日期: 2021-04-11 23:19:42
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20201024053147AAdvphP