# Thread: trig substitution

1. ## trig substitution

suggest an appropriate trig substitution for x in

int(x^5/(x^2-5)^3/2)dx
and
int((3-x^2)^5/2)dx

2. Originally Posted by samdmansam
suggest an appropriate trig substitution for x in

int(x^5/(x^2-5)^3/2)dx
$\displaystyle x = \sqrt{5} \sec \theta$

int((3-x^2)^5/2)dx
$\displaystyle x = \sqrt{3} \sin \theta$

3. The first one is also solvable by standard algebraic techniques.

4. Originally Posted by Krizalid
The first one is also solvable by standard algebraic techniques.
you mean a regular substitution of $\displaystyle u = x^2 - 5$, or something else?

yes, that regular substitution will do it, but the poster asked for a trig substitution, so ...

[off-topic]

what happened to your other badge, Krizalid?

[/off-topic]

5. Yeah, but observe that I said "also."

As for my another badge, I personally asked to be removed.

6. Originally Posted by Krizalid
Yeah, but observe that I said "also."
were you thinking about what i suggested, or something else?

As for my another badge, I personally asked to be removed.
really? how come? the badges getting too heavy?