此题有误，应为：已知a + 1/a = 5 求: a2/a4+ a2 + 1的值
解;a + 1/a = 5
（a + 1/a )^2=25
a^2/a^4 + a^2 +2=25
a^2/a^4+ a^2 =23
a^2/a^4 + a^2 +1 =24
a + 1/a = 5 (*a)
a^2 + 1 = 5a
a^2 = 5a-1
a^4/a^2 + a^2 +1 = 0
a^(4-2) + a^2 + 1 = 0
2 a^2 + 1 = 0 , (a^2 = 5a-1)
2(5a - 1) + 1 = 0
10a - 2 + 1 = 0
10a - 1 = 0
10a = 1
a = 1/10
a4/a2 + a2 + 1 看不懂 分子,分母各是什么,没有括号,看不明白
答：解:a+1/a=5,则(a+1/a)^2=5^2,a^2+1/a^2=23. (a^4+a^2+1)/a^2………………(分式的分子与分母同除以a^2) =(a...详情>>
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