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Exercise: Standard Forms — Square Roots · Q26

Q.Evaluate ∫dxx2+6x+13\displaystyle\int \frac{dx}{\sqrt{x^2+6x+13}}.

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✓ Free question

Complete the square: x2+6x+13=(x+3)2+22x^2+6x+13=(x+3)^2+2^2. With u=x+3u=x+3, a=2a=2, Section 6's log formula

gives

∫dxx2+6x+13=∫duu2+4=ln⁡∣u+u2+4∣+C=ln⁡∣(x+3)+x2+6x+13∣+C.\int\frac{dx}{\sqrt{x^2+6x+13}} = \int\frac{du}{\sqrt{u^2+4}} = \ln\left|u+\sqrt{u^2+4}\right|+C = \ln\left|(x+3)+\sqrt{x^2+6x+13}\right|+C.

Check: by the same pattern as Q1, shifted by x→x+3x\to x+3: differentiating reproduces

1/(x+3)2+4=1/x2+6x+131/\sqrt{(x+3)^2+4}=1/\sqrt{x^2+6x+13}.

✓Final answer

∫dxx2+6x+13=ln⁡∣(x+3)+x2+6x+13∣+C\int\dfrac{dx}{\sqrt{x^2+6x+13}}=\ln\left|(x+3)+\sqrt{x^2+6x+13}\right|+C

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