Tuesday

September 16, 2014

September 16, 2014

Posted by **Marissa** on Friday, August 15, 2008 at 1:31am.

This is what I did:

Let u = π/x

(to get the derivative and du:)

π*1/x

π(-1/x^2)dx = du

π(1/x^2)dx = (-1)du

so, 1/x^2 = -1/πdu

then ∫ [sin (π/x)]/ x^2] dx = ∫ sin(u) (-1/π)du

= -1/π ∫ sin u du

= -1/π (-cos u) + C

= 1/π (cos u) + C

sub back in:

1/π cos (π/x) + C

I'm unsure of this because I don't know if I got du the right way.

Should it have been

Let u = π/x

-π/x^2 dx = du

1/x^2 dx = -πdu

That would make the answer a lot different...

Help!

- Math integrals -
**drwls**, Friday, August 15, 2008 at 1:45amYour first derivation is correct.

The last equation you wrote does not follow from (-π/x^2) dx = du

You did it right the first time

**Answer this Question**

**Related Questions**

Math, please help - Which of the following are trigonometric identities? (Can be...

Math - Evaluate *Note - We have to find the exact value of these. That I know to...

Precalculus - Use one of the identities cos(t + 2πk) = cos t or sin(t + 2&#...

Trig Help! - Question: Trying to find cos π/12, if cos π/6 = square ...

Calculus - How do I find the critical values? y= 4/x + tan(πx/8) What I ...

Trig - find all solutions to the equation √3 csc(2theta)=-2 Would the ...

Math 2nd question - Express as a single sine or cosine function (note: this is ...

Math - Can you help me with this? I did this many times and got different ...

geometry/algebra - I asked this question yesterday, and I'm trying to understand...

Calculus - an open topped cylinder has a volume of 125 cubic inches. determine ...