(1) y = x^3/(x^2+3) = (x^3+3x-3x)/(x^2+3) = x - 3x/(x^2+3)
y' = 1 - 3(3-x^2)/(x^2+3),
y'' = 3[-2x(x^2+3)-2x(3-x^2)]/(x^2+3) = -36x/(x^2+3)
å¹åºé´ xâ(-â, 0), å¸åºé´ xâ(0, +â), æç¹ O(0, 0) .
(3) y' = (8/3)x^(5/3) - (5/3)x^(2/3)
y'' = (40/9)x^(2/3) - (10/9)x^(-1/3)
= (10/9)(4x-1)/x^(1/3)
令 y'' = 0, å¾ x = 1/4, äºé¶å¯¼æ°ä¸åå¨çç¹æ¯ x = 0.
å¹åºé´ xâ(-â, 0)âª(1/4, +â) , å¸åºé´ xâ(0, 1/4),
æç¹ O(0, 0) . P(1/4, -3/16^(4/3))
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