Is the solution for trig substitution correct?

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In summary, trig substitution is a technique used in calculus to simplify integrals involving certain types of functions. It is typically used when there are expressions involving x, a^2-x^2, or x^2-a^2, as well as square roots or inverse trigonometric functions present. The steps for performing trig substitution include identifying the type needed, making the substitution, simplifying the integral, integrating the simplified expression, and converting back to the original variable. It is not effective for all integrals and other techniques may be necessary. To check if the solution is correct, you can differentiate it or use a graphing or online calculator to compare it to the original integral.
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nameVoid
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Homework Statement


I(1/(9x^2+6x-8)^(1/2),x)
I( 1/( (3x+1)^2-9 )^(1/2),x )
3x+1=3secT
dx=secTtanTdT
I( (secTtanT)/3tanT,T )
(1/3)I( secT,T)
(1/3)|secT+tanT|+C
secT=(3x+1)/3
tanT=(9x^2+6x-8)^(1/2)/3
solution: (1/3)|(3x+1)/3+(9x^2+6x-8)^(1/2)/3|
my book is showing :(1/3)|(3x+1)+(9x^2+6x-8)^(1/2)|


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  • #2
nameVoid said:

Homework Statement


I(1/(9x^2+6x-8)^(1/2),x)
I( 1/( (3x+1)^2-9 )^(1/2),x )
3x+1=3secT
dx=secTtanTdT
I( (secTtanT)/3tanT,T )
(1/3)I( secT,T)
(1/3)|secT+tanT|+C
secT=(3x+1)/3
tanT=(9x^2+6x-8)^(1/2)/3
solution: (1/3)|(3x+1)/3+(9x^2+6x-8)^(1/2)/3|
my book is showing :(1/3)|(3x+1)+(9x^2+6x-8)^(1/2)|

Double-check these steps.
 

1. What is trig substitution and why is it used?

Trig substitution is a technique used in calculus to solve integrals involving certain types of functions, such as those containing radicals or inverse trigonometric functions. It is used to simplify the integral and make it easier to solve.

2. How do I know when to use trig substitution?

Trig substitution is typically used when there is an expression involving x, a^2-x^2, or x^2-a^2 in the integrand. It is also used when there are square roots or inverse trigonometric functions present.

3. What are the steps for performing trig substitution?

The steps for performing trig substitution are as follows:

  1. Identify the type of trig substitution needed based on the expression in the integrand.
  2. Make the appropriate substitution, using trigonometric identities if necessary.
  3. Simplify the integral using algebra and trigonometric identities.
  4. Integrate the simplified expression.
  5. Convert back to the original variable.

4. Can I use trig substitution to solve any integral?

No, not all integrals can be solved using trig substitution. It is most effective for integrals containing certain types of functions, as mentioned in the first question. Other techniques, such as integration by parts or partial fractions, may be necessary for other types of integrals.

5. How do I know if my solution for trig substitution is correct?

You can check if your solution is correct by differentiating it and seeing if the result matches the original integrand. You can also verify your answer by using a graphing calculator or online integral calculator to evaluate the original integral and comparing it to your solution.

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