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Evaluate the integral and express your answer in simplest form.

int(-9)/(xsqrt(x^(2)-25))dx
Answer:

Evaluate the integral and express your answer in simplest form.\newline9xx225dx \int \frac{-9}{x \sqrt{x^{2}-25}} d x \newlineAnswer:

Full solution

Q. Evaluate the integral and express your answer in simplest form.\newline9xx225dx \int \frac{-9}{x \sqrt{x^{2}-25}} d x \newlineAnswer:
  1. Identify Integral: Let's identify the integral we need to evaluate:\newlineI=9xx225dxI = \int \frac{-9}{x\sqrt{x^2-25}} \, dx\newlineTo solve this integral, we can use a trigonometric substitution. Let x=5sec(θ)x = 5\sec(\theta), which implies dx=5sec(θ)tan(θ)dθdx = 5\sec(\theta)\tan(\theta) \, d\theta. When x=5sec(θ)x = 5\sec(\theta), x225\sqrt{x^2-25} becomes 25sec2(θ)25=5tan(θ)\sqrt{25\sec^2(\theta)-25} = 5\tan(\theta).
  2. Trigonometric Substitution: Substitute x=5sec(θ)x = 5\sec(\theta) and dx=5sec(θ)tan(θ)dθdx = 5\sec(\theta)\tan(\theta) d\theta into the integral:\newlineI=95sec(θ)5tan(θ)5sec(θ)tan(θ)dθI = \int\frac{-9}{5\sec(\theta)*5\tan(\theta)} * 5\sec(\theta)\tan(\theta) d\theta\newlineSimplify the integral:\newlineI=95dθI = \int\frac{-9}{5} d\theta
  3. Substitute and Simplify: Integrate with respect to θ\theta:I=(95)θ+CI = \left(-\frac{9}{5}\right)\theta + C, where CC is the constant of integration.
  4. Integrate with Respect: Now we need to express θ\theta in terms of xx to get back to the original variable. From x=5sec(θ)x = 5\sec(\theta), we have sec(θ)=x5\sec(\theta) = \frac{x}{5}. Taking the arccosine of both sides, we get θ=sec1(x5)\theta = \sec^{-1}(\frac{x}{5}).
  5. Express in Terms of x: Substitute θ\theta back into the integral result: I=(95)sec1(x5)+CI = \left(-\frac{9}{5}\right)\sec^{-1}\left(\frac{x}{5}\right) + C This is the simplest form of the integral in terms of xx.