Q. Evaluate the integral and express your answer in simplest form.∫xx2−363dxAnswer:
Recognize integral form: Let's start by recognizing that the integral resembles the form of the derivative of an inverse trigonometric function, specifically the inverse hyperbolic function. We can use a substitution to simplify the integral. Let's set x=6sec(θ), which implies dx=6sec(θ)tan(θ)dθ. When x=6, θ=0, and as x approaches infinity, θ approaches 2π. The integral becomes:∫xx2−363dx=∫6sec(θ)36sec2(θ)−363⋅6sec(θ)tan(θ)dθ
Simplify with substitution: Simplify the integral by substituting x=6sec(θ) and dx=6sec(θ)tan(θ)dθ:∫6sec(θ)36sec2(θ)−363⋅6sec(θ)tan(θ)dθ= ∫6sec(θ)36(sec2(θ)−1)3⋅6sec(θ)tan(θ)dθ= ∫6sec(θ)36tan2(θ)3⋅6sec(θ)tan(θ)dθ= ∫636tan(θ)3⋅6sec(θ)tan(θ)dθ= ∫6⋅6tan(θ)3⋅6sec(θ)tan(θ)dθ= ∫36tan(θ)3⋅6sec(θ)tan(θ)dθ= ∫61sec(θ)dθ
Integrate secant function: Now we integrate (61)sec(θ)dθ:\int(\frac{\(1\)}{\(6\)})\sec(\theta)d\theta = (\frac{\(1\)}{\(6\)})\ln|\sec(\theta) + \tan(\theta)| + C
Back-substitute for x: We need to back-substitute to return to the original variable x. From our substitution, we have \(x = 6\sec(\theta), so sec(θ)=6x. Also, tan(θ)=6x2−36. Therefore, the integral in terms of x is:\frac{\(1\)}{\(6\)}\ln|\sec(\theta) + \tan(\theta)| + C\(\newline= \frac{1}{6}\ln|\left(\frac{x}{6}\right) + \left(\frac{\sqrt{x^2−36}}{6}\right)| + C= \frac{1}{6}\ln|\frac{x + \sqrt{x^2−36}}{6}| + C= \frac{1}{6}\ln|x + \sqrt{x^2−36}| - \frac{1}{6}\ln(6) + C
Combine constant terms: We can combine the constant terms into a single constant of integration:(\frac{1}{6})\ln|x + \sqrt{(x^2-36)}| - (\frac{1}{6})\ln(6) + C\(\newline= (\frac{1}{6})\ln|x + \sqrt{(x^2-36)}| - \ln(6^{(\frac{1}{6})}) + C= (\frac{1}{6})\ln|x + \sqrt{(x^2-36)}| + C'\)where C′ is a new constant of integration that absorbs the −ln(6(61)) term.
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