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Question 229 of 255

Q.Prove that: ∫1a2−x2 dx=12alog⁡∣a+xa−x∣+c\displaystyle\int \dfrac{1}{a^2-x^2}\,dx = \dfrac{1}{2a}\log\left|\dfrac{a+x}{a-x}\right| + c.

Maharashtra MsbshseMaharashtra HSC (MSBSHSE) Board 2018Subjective· 4mImportance★★★★★
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Decompose 1a2−x2\dfrac{1}{a^2-x^2} into partial fractions using a2−x2=(a−x)(a+x)a^2-x^2=(a-x)(a+x), then integrate term by term.

Since a2−x2=(a−x)(a+x)a^2-x^2 = (a-x)(a+x), decompose into partial fractions:

1a2−x2=1(a−x)(a+x)=12a[1a−x+1a+x]\frac{1}{a^2-x^2} = \frac{1}{(a-x)(a+x)} = \frac{1}{2a}\left[\frac{1}{a-x}+\frac{1}{a+x}\right]

(Check: 12a[1a−x+1a+x]=12a⋅(a+x)+(a−x)(a−x)(a+x)=12a⋅2aa2−x2=1a2−x2\dfrac{1}{2a}\left[\dfrac{1}{a-x}+\dfrac{1}{a+x}\right] = \dfrac{1}{2a}\cdot\dfrac{(a+x)+(a-x)}{(a-x)(a+x)} = \dfrac{1}{2a}\cdot\dfrac{2a}{a^2-x^2}=\dfrac{1}{a^2-x^2} ✓)

Integrating both sides: …

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