我是高一生 可以教我這一數學題嗎?

2016-09-20 11:32 am

回答 (1)

2016-09-21 10:42 pm
✔ 最佳答案
考慮 (∛4 + 3∛2 + 1) (a∛4 + b∛2 + c)
= a∛16 + (3a + b)∛8 + (a + 3b + c)∛4 + (b + 3c)∛2 + c
= (a + 3b + c)∛4 + (2a + b + 3c)∛2 + 6a + 2b + c

令 a + 3b + c = 2a + b + 3c = 0 ⇒ 3a + 9b + 3c - (2a + b + 3c) = 0 ⇒ a + 8b = 0 ,
取 a = 8 , b = - 1 , 則 c = - 5 , 於是 (∛4 + 3∛2 + 1) (8∛4 - ∛2 - 5) = 6(8) + 2(-1) + (-5)
⇒ 1 / (∛4 + 3∛2 + 1) = (8∛4 - ∛2 - 5) / 41


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