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Exercise: Standard Forms — Algebraic ... · Q23

Q.Evaluate ∫dx4x2+4x+5\displaystyle\int \frac{dx}{4x^2+4x+5}.

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Factor out 44: 4x2+4x+5=4(x2+x)+5=4(x+12)2+44x^2+4x+5=4\big(x^2+x\big)+5=4\big(x+\tfrac12\big)^2+4 (since

4(x+12)2=4x2+4x+14(x+\tfrac12)^2=4x^2+4x+1, and 1+4=51+4=5). So

∫dx4x2+4x+5=∫dx4(x+12)2+4=14∫dx(x+12)2+1=14tan⁡−1 ⁣(x+12)+C.\int\frac{dx}{4x^2+4x+5} = \int\frac{dx}{4\big(x+\tfrac12\big)^2+4} = \frac14\int\frac{dx}{\big(x+\tfrac12\big)^2+1} = \frac14\tan^{-1}\!\left(x+\frac12\right)+C. …

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