Calculus 2 : Solving Integrals by Substitution

Study concepts, example questions & explanations for Calculus 2

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Example Questions

Example Question #81 : Solving Integrals By Substitution

Calculate the following integral: 

Possible Answers:

Correct answer:

Explanation:

Solve via integration by parts. Make the following substitutions:

    .

Plug in substitutions: .

Solve via integration by parts again. Make the following substitutions:

      .

Plug in substitutions: .

Simplify: .

Plug this integral back into our original equation:

Simplify: .

Add  to both sides of the equation: .

Factor  out of the right side of the equation: 

Divide both sides of the equation by 

Example Question #1011 : Integrals

Calculate the following integral: 

Possible Answers:

Correct answer:

Explanation:

Factor out a sinx:

Apply Pythagorean identity to .

Making the following substitutions:   

Apply substitutions: 

Solve integral: 

Convert u back to x: 

Example Question #2761 : Calculus Ii

Calculate the following integral: 

Possible Answers:

Correct answer:

Explanation:

Make the following substitution:  .

Plug the substitution into the integrand: .

Factor out  from the denominator, and simplify: .

Apply Pythagorean identity to the denominator, and simplify:.

Solve integral:.

Use original substitution to solve for        

Plug value for  back into solution for integral: .

Example Question #2761 : Calculus Ii

Evaluate the following indefinite integral: 

Possible Answers:

Correct answer:

Explanation:

This integral, , is a classic integration by substation problem. This is indicated by the presence of a composite function in which both a function and its derivative are present. 

For this we need to let our variable  , substituting this into our integral we produce the following:

and by substituting back in for u we find our final answer to be:
.

Example Question #84 : Solving Integrals By Substitution

Evaluate the integral and use the sine function to make an appropriate trigonometric substitution. 

 

Possible Answers:

Correct answer:

Explanation:

                                                    (1)

 

To compute this integral we will use a trigonometric substitution. First we need to do some algebra to write the integrated in a more suitable form, 

 

                                               (2)

 

Now we can apply a trigonometric substitution. 

                                                   (3)

                                         (4)

 

 

Notice we've chosen this substitution so that the radicand in equation (2) will conveniently reduce as follows, 

 

  

 

So now we have  , we need to convert back to , use equation (3), 

 

 

Example Question #671 : Finding Integrals

Integrate

 



Possible Answers:

Correct answer:

Explanation:

                                                       (1)

1) Simplify with a substitution. 

It is often necessary to define a new variable , carefully chosen so that rewriting the integrand in terms of this new variable will make integration easier. In this case, the obvious variable to introduce will be defined by, 

                                                                      (2)

                                                                         (3)

 

Use equations (2) and (3) to rewrite (1).  

 

 

 2) Use integration by parts

To compute  use integration by parts. Ignore the constant out front for the moment, 

 

                                                 (4)

Define  and  and insert into the equation (4). 

  

 ,

 

 

 

 

                                               (5)

 

Let's factor the non-constant terms in equation (5), this will make the result easier to express when we convert back to 

 

We previously had a constant in front of the integral, 

 

 

Now we can write the integral terms of the original variable  by substituting equation (2) into the previous expression to obtain, 

 

 

 

Example Question #671 : Finding Integrals

Evaluate the integral:

Possible Answers:

Correct answer:

Explanation:

To evaluate the integral, we perform the following substitution:

The derivative was found using the following rule:

Now, we rewrite the integrand and integrate:

The integral was performed using the following rule:

Finally, replace u with our original x term:

Example Question #1022 : Integrals

The Laplace Transform is an integral transform that converts functions from the time domain  to the complex frequency domain . The transformation of a function  into its complex frequency function   is given by:

Where , where  and  are constants and  is the imaginary number. 

Evaluate the Laplace Transform of the function  at time . Suppose that  when 

Possible Answers:

Correct answer:

Explanation:

The Laplace Transform will be given by:

Since  when , we can change the integral to:

 

This is because when you change the lower bound of the integral, the exponent will only exist for values for which  is defined. 

Let 

This changes our integral to:

We can now move the  term out of the integral, which will give us:

Example Question #1021 : Integrals

Evaluate the following integral using substitution:

Possible Answers:

Correct answer:

Explanation:

To evaluate this integral, we first make the following substitution:

Differentiating this expression, we get:

Now, we can rewrite the original integral with our substitution and solve:

Finally, we have to replace with our earlier definition:

Example Question #1024 : Integrals

In exponentially decaying systems, often times the solutions to differential equations take on the form of an integral called Duhamel's Integral. This is given by:

Where  is a constant and  is a function that represents an external force. 

Suppose I introduce growth factors that effect my population at a rate of 

. At what rate  do I need in order for my population to grow? (Hint: Find  and determine for what  will  increase in time.)

Possible Answers:

Correct answer:

Explanation:

Start by substituting  into the integral to get:

We can combine this into one large term:

Since .

This can only grow when: 

 

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