Mark M. answered 08/27/18
Tutor
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Retired math prof. Calc 1, 2 and AP Calculus tutoring experience.
Let u = x3 So, du = 3x2dx
x2dx = (1/3)du
Then, the given integral is equivalent to (1/3)∫du / (1+u2)
= (1/3)Tan-1u + C
= (1/3)Tan-1(x3) + C