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Evaluate: ∫ 2x x2 + 1 x2 + 3 dx
I = ∫ 2 x x2 + 1 x2 + 3 dxLet x2 = z∴ 2 x dx = dz∴ I = ∫ dz z + 1 z + 3
By partial fraction,
1 z + 1 z + 3 = A z + 1 + B z + 3 ⇒ 1 = A z + 3 + B z + 1 Putting z = - 3, we obtain:1 = - 2 BB = - 12∴ A = 12∴ 1 z + 1 z + 3 = 12 z + 1 + - 12 z + 3⇒ ∫ dz z + 1 z + 3 = 12 ∫ dz z + 1 - 12 ∫ dz z + 3 = 12 log z + 1 - 12 log z + 3 + C∴ ∫ 2 x dx x2 + 1 x2 + 3 = 12 log x2 + 1 - 12 log x2 + 3 + C
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