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Given the integral of (1/(1+9x^2)dx taking u =3x.
Use integration by substitution

User Phil Frost
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1 Answer

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u = 3x
du = 3dx => dx = 1/3 du
Integral of (1 / (1 + 9x^2))dx = 1/3 (integral (1/(1 + u^2))du) = 1/3 arctan(u) + c = 1/3 arctan (3x) + c
User Peter Sirka
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