A community for students.
Here's the question you clicked on:
 0 viewing
baldymcgee6
 2 years ago
Use an inverse trig substitution on the integral...
baldymcgee6
 2 years ago
Use an inverse trig substitution on the integral...

This Question is Closed

baldymcgee6
 2 years ago
Best ResponseYou've already chosen the best response.1dw:1358909488344:dw

abb0t
 2 years ago
Best ResponseYou've already chosen the best response.0For inverse trig function, you want to get it into a form that looks like arctan, arcsin, arcos, etc., The first step is to complete the square.

baldymcgee6
 2 years ago
Best ResponseYou've already chosen the best response.1complete the square in the denominator... okkkk

baldymcgee6
 2 years ago
Best ResponseYou've already chosen the best response.1you're going to have to refresh my memory on how to do that :/

baldymcgee6
 2 years ago
Best ResponseYou've already chosen the best response.1dw:1358910770499:dw

abb0t
 2 years ago
Best ResponseYou've already chosen the best response.0\[ax^2+bx+c \] \[(\frac{ b }{ 2 })^2 \]

baldymcgee6
 2 years ago
Best ResponseYou've already chosen the best response.1i'm sorry, i forget what to do...

abb0t
 2 years ago
Best ResponseYou've already chosen the best response.0divide by two and square the answer of the 2nd term (b).

baldymcgee6
 2 years ago
Best ResponseYou've already chosen the best response.1dw:1358910964480:dw

abb0t
 2 years ago
Best ResponseYou've already chosen the best response.0Yeah. Now, you can factor it to get something that looks like an inverse trig, so that you get: \[(x \pm a)^2 + 1\] where you will tell what inverse trig function you have. Try it.

abb0t
 2 years ago
Best ResponseYou've already chosen the best response.0Essentially, you might need to do more work, like factor out a number or two. But remember that you have it in a square root! so I think it might be arcos? Just a guess. It wont be arctan since arctan does;t have a square root.

baldymcgee6
 2 years ago
Best ResponseYou've already chosen the best response.1dw:1358914184400:dw@abb0t

baldymcgee6
 2 years ago
Best ResponseYou've already chosen the best response.1i don't see where that takes us.

baldymcgee6
 2 years ago
Best ResponseYou've already chosen the best response.1dw:1358914405152:dw

zepdrix
 2 years ago
Best ResponseYou've already chosen the best response.1Let's not do a Usub, that seems rather unnecessary. We'll already be doing a trig sub, so it's better if we can limit the number of substitutions that we apply. Your factoring looks good. So we're at this point.\[\large \int\limits\frac{dx}{\left[2(x1)^23\right]^{3/2}}\]

zepdrix
 2 years ago
Best ResponseYou've already chosen the best response.1Ok this next part is going to be a little tricky to understand, let me see if I can put it into the right words. There are 3 primary forms that we look for when making a trig sub. We'll look at the one that specifically applies to this problem. Ignore the 2 coefficient on X in the bottom for a moment. Our intention is to get rid of the addition or subtraction in the bottom. If we can do that, simplify it down to ONE term, we can easily apply the exponent on the outside to it. If we see:\[\large x^2a^2\]We want to let \(\large x=a\sec \theta\) That will do this for us,\[\large x^2a^2 \qquad \rightarrow \qquad a^2\sec^2 \thetaa^2 \qquad \rightarrow \qquad a^2(\sec^2\theta1)\] From there, we can recall that \(\large \sec^2\theta1=tan^2\theta\) and make the switch. \[\large a^2(\tan^2\theta)\] Now you might be saying, "But zep! We don't have an a^2! We just have a 3!" Well baldy this is where it gets a little tricky. We need to get that ugly 2 off of our x term.\[\large \int\limits\limits\frac{dx}{\left[2\left((x1)^2\dfrac{3}{2}\right)\right]^{3/2}}\]

zepdrix
 2 years ago
Best ResponseYou've already chosen the best response.1"But zep! We still don't have a nice \(a\) value!" Well that's just the way it works out sometimes. We DO have an \(a\), it's just a little ugly :D So in our case, our \(a\) value is going to be \(\dfrac{\sqrt3}{\sqrt2}\).

zepdrix
 2 years ago
Best ResponseYou've already chosen the best response.1We'll make the following substitution, \[\large (x1)=\frac{\sqrt3}{\sqrt2}\sec \theta\] So our denominator will do something like this, \[\large \left[2\left(\color{salmon}{(x1)^2}\dfrac{3}{2}\right)\right]^{3/2} \qquad \rightarrow \qquad \left[2\left(\color{salmon}{\frac{3}{2}\sec^2\theta}\frac{3}{2}\right)\right]^{3/2}\]

zepdrix
 2 years ago
Best ResponseYou've already chosen the best response.1\[\large \left[3\left(\sec^2\theta1\right)\right]^{3/2} \qquad \rightarrow \qquad \left[3\left(\tan^2\theta\right)\right]^{3/2}\]Which simplifies to,\[\large \sqrt{27}\tan^3 \theta\]

zepdrix
 2 years ago
Best ResponseYou've already chosen the best response.1Giving us an integral of,\[\large \frac{1}{\sqrt{27}}\int\limits\frac{dx}{\tan^3\theta}\]From here, we'll still need to deal with the dx.

zepdrix
 2 years ago
Best ResponseYou've already chosen the best response.1\[\large (x1)=\frac{\sqrt3}{\sqrt2}\sec \theta \qquad \rightarrow \qquad dx=\frac{\sqrt3}{\sqrt2}\sec\theta\tan\theta \; d \theta\] So our integral becomes,\[\large \frac{1}{\sqrt{27}}\cdot\frac{\sqrt3}{\sqrt2}\int\limits\limits\frac{\sec \theta \tan \theta \; d \theta}{\tan^3\theta}\]

zepdrix
 2 years ago
Best ResponseYou've already chosen the best response.1So from here, cancel out a couple of tangents. Then convert everything to sines and cosines. At that point you'll have a couple options. You can do a nice easy Usub, Or You can write your terms as \(\cot\theta \csc\theta\) which is a fairly easy integral.

zepdrix
 2 years ago
Best ResponseYou've already chosen the best response.1There a bit more to be done to get through this. But I'm tired, and you're offline anyway XD lol.
Ask your own question
Sign UpFind more explanations on OpenStudy
Your question is ready. Sign up for free to start getting answers.
spraguer
(Moderator)
5
→ View Detailed Profile
is replying to Can someone tell me what button the professor is hitting...
23
 Teamwork 19 Teammate
 Problem Solving 19 Hero
 Engagement 19 Mad Hatter
 You have blocked this person.
 ✔ You're a fan Checking fan status...
Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.