Thursday, 10 December 2015

Integral of ∫dx/sqrt(a^2 + x^2)


The integral ∫dx/√(a2 + x2) may be approached in 2 ways:

1. Trigonometric substitution, or
2. Hyperbolic substitution

The goal of both methods is to simplify the denominator expression: √(a2 + x2).

With trigonometric substitution, we can let x = atanθ, and thus dx = asec2θdθ, and √(a2 + x2) simplifies to √[a2(1 + tan2θ)] = asecθ. And the integral becomes ∫secθdθ.

With hyperbolic substitution, we can let x = asinhu, and thus dx = acoshudu, and √(a2 + x2) simplifies to √[a2(1 + sinh2u)] = acoshu, so the integral becomes ∫du.

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