f(x)=x^3-3ax-1,
f'(x)=3x^2-3a=3(x^2-a)
当a>0时
由x^2-a≥0
得x≥√ a或x≤ -√ a,f(x)单调递增区间为[根号a,+无穷)和(-无穷,-根号a]
由x^2-a≤0
得-√ a≤x≤ √ a,f(x)单调递减区间为[-根号a,根号a]
,当a0恒成立
x属于R,f(x)单调递增区间为(-无穷,+无穷),无单调递减区间
f(x)=x^3-3ax-1,
f'(x)=3x^2-3a=3(x^2-a)
当a>0时
由x^2-a≥0
得x≥√ a或x≤ -√ a,f(x)单调递增区间为[根号a,+无穷)和(-无穷,-根号a]
由x^2-a≤0
得-√ a≤x≤ √ a,f(x)单调递减区间为[-根号a,根号a]
,当a0恒成立
x属于R,f(x)单调递增区间为(-无穷,+无穷),无单调递减区间