The monotonicity of function f (x) = 1 / 3x3 + ax & # 178; + X + 1 is discussed
f’(x)=x^2+2ax+1
△=4a^2-4=4(a+1)(a-1)
① When △≤ 0,
That is - 1 ≤ a ≤ 1,
There are f '(x) ≥ 0,
So f (x) is increasing in R
② When △ > 0
A1,
If x-a + √ (a ^ 2-1)
Then f '(x) > 0, f (x) increases singly
If - A - √ (a ^ 2-1)
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