Q. Evaluate the integral and express your answer in simplest form.∫xx2−93dxAnswer:
Recognize standard inverse trigonometric form: Recognize the integral as a standard inverse trigonometric form.The integral resembles the form of the derivative of the inverse hyperbolic function, specifically the inverse hyperbolic secant. We can rewrite the integral in a form that matches the derivative of arcsinh(x/a) or arcsech(x/a).I=∫xx2−93dx
Use substitution to simplify: Use substitution to simplify the integral. Let x=3sec(θ), which implies dx=3sec(θ)tan(θ)dθ. When x=3sec(θ), we have x2−9=9sec2(θ)−9=3tan(θ). Now substitute these into the integral. I=∫3sec(θ)∗3tan(θ)3∗3sec(θ)tan(θ)dθ
Simplify the expression: Simplify the expression.The 3sec(θ)tan(θ) terms cancel out, leaving us with:I=∫tan(θ)1dθ
Recognize natural logarithm function: Recognize the integral as the natural logarithm function.The integral of tan(θ)1 is the natural logarithm of the absolute value of sin(θ).I=ln∣sin(θ)∣+C, where C is the constant of integration.
Back-substitute to original variable: Back-substitute to return to the original variable x. We need to express sin(θ) in terms of x. From the substitution x=3sec(θ), we have cos(θ)=x3. Since sin2(θ)+cos2(θ)=1, we can solve for sin(θ)=1−cos2(θ)=1−(x3)2. I=ln∣1−(x3)2∣+C
Simplify expression inside logarithm: Simplify the expression inside the logarithm.We can simplify the square root and the square inside the logarithm.I=ln∣1−9/x2∣+CI=ln∣x1⋅x2−9∣+C
Simplify logarithm expression: Simplify the logarithm expression.Since ln(a⋅b)=ln(a)+ln(b), we can separate the terms inside the logarithm.I=ln∣∣x1∣∣+ln∣∣x2−9∣∣+C
Combine constants into single constant: Simplify further using properties of logarithms.The natural logarithm of a square root is one-half the natural logarithm of the argument, and ln∣x1∣ is −ln∣x∣.I=−ln∣x∣+21⋅ln∣x2−9∣+C
Combine constants into single constant: Simplify further using properties of logarithms.The natural logarithm of a square root is one-half the natural logarithm of the argument, and ln∣x1∣ is −ln∣x∣.I=−ln∣x∣+21⋅ln∣x2−9∣+CCombine the constants into a single constant of integration.Since C is an arbitrary constant, we can combine the constants from the logarithm properties into a single constant.I=−ln∣x∣+21⋅ln∣x2−9∣+C
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