# Hey, Veeky Forums

Hey, Veeky Forums. I tried evaluating this integral using trig sub, but it didn’t work. Can someone tell me why? (This is not a homework question, I just had a doubt)

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bump.

If you look closely there's a solution and explanation right below the question. Hope this helps!

I know, but I wanted to try it out with trig substitution and it didn’t work out. I don’t want to know the solution, I want to know why trig sub doesn’t work

And what trig substitution are you going to use for that?

I have this Phillips head screw and the right screwdriver right here, but I really want to use a wrench. Why won't it work?

square root x = tan^2 (theta)

You can get answers with more than one method. That's not a very good analogy.

Ur implying math is consistent

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it's not in the right form to use a trig sub. now go post this on /wsr/ or something. one calc II problem isn't really worth a thread

OP here. I just checked and trig sub does work. It gives you a different function, but the resulting graph is the same in both cases.

I got this result for your sub:
$\sqrt{x}= \tan^2 \theta$
gives you the integral of
$\sin^3 \theta \cos \theta~d \theta$

thats the problem, at this point you have to use a u-sub anyway, so why not just use it to begin with instead of a trig sub

just a demonstration of what Grandpa used to say:
there is more than one way to skin a cat

OP here. That's what I got. The final answer is sin^4 (theta)

It probably sounds weird, but its easier for me this way

The final answer is sin^4 (theta)
That's not the final answer though. How do you intend to bring this back into terms of $x$?

x/((1 + sqrtx)^2)?

You're saying $\int \frac{dx}{(1+\sqrt x)^3} = \sin^4 \theta$. Your final answer shouldn't be in terms of $\theta$ when the question is in terms of $x$.

I know, I phrased it wrong. My bad.

why the fuck would you simplify with trig?
just use x = u^2 to get it to be 2u/(1+u)^3, then add 0 = 2 - 2, getting (2u + 2)/(1+u)^3 - 2/(1+u)^3, which simplifies to 2/(1+u)^2 - 2/(1+u)^3. Then use the substitution u = w - 1 to get 2/w^2 - 2/w^3, from there, its absolutely basic
i have no idea why anybody would use trig on this problem

See:

It's not a homework problem because I SAID SO!
Fuck off, nigger.