# Homework Help: Antiderivative of 1.4x*cos(x^1.9)

1. Mar 17, 2008

### momogiri

Question

f'(x) = 1.4x*cos(x^1.9)
Find f(x)

Attempt
Ok, first of all, I'm really bad at Calculus, so bear with me >__<
I figured to find the antiderivative of the thing is equivalent to
$$\int\left1.4x*cos\leftx^{1.9}\right\right)dx$$

I've tried simple substitution (u = x^1.9) and that obviously doesn't work, and I tried integration by parts, but I don't think it's working
If I had dv = cos(x^1.9)dx
I'm unsure if I can find v when x is x^1.9

Help will be appreciated! Thanks!

Last edited: Mar 17, 2008
2. Mar 17, 2008

### Deviatorz

Your doing the math lab arn't you? I have the same problem except my f'(x) = 1.7x*sin(x^1.8)

3. Mar 17, 2008

### rocomath

You have two different Integrals ... which is it?

$$\int1.4x\cos{x^{1.9}}dx$$

or

$$\int1.4x\cos^{1.9}xdx$$

Does the power belong to cosine or the variable x?

4. Mar 17, 2008

### qspeechc

Have you tried Taylor expansion? That's all I can think of now.

5. Mar 17, 2008

### Snazzy

If you're doing the mathlab for a UBC math course *cough*, then use the spreadsheet.