Second Partial Differentiation Problem

Töpher

Hey,

Studying for repeat exams in Maths at the moment (4 fecking exams! :mad: ), bit stuck with Calculus at the moment.
Some of the questions involve second partial derivatives, thats fine. I understand and can do all that, depending on the equation given. If the equation invloves -sin/tan/cos its fine, and I can figure it all out. But if it includes exp or log10 I'm boned! Haven't a clue what they differentiate to, nevermind what their differentiations differentiate to! Tried looking online, to no avail, so just figured I'd ask here on the off chance.

Thanks.

John

Bugger, I used to know this. I can check for you tonight if it's not too late?

Isn't the derivative of an exp = exp?

de^x/dx=e^x?

DapperGent

Einst&#252 wrote: »

But if it includes exp or log10 I'm boned! Haven't a clue what they differentiate to, nevermind what their differentiations differentiate to! Tried looking online, to no avail, so just figured I'd ask here on the off chance.

The rules should all be in a copy of the log tables and you partially differentiate them the same way you do anything else. Differentiate x treat y as a constant etc.

f(x,y) = (y)exp(5x)
df/dx = (5y)exp(5x) .......... (I think, haven't done them in a while)
df/dy = exp(5x)

Töpher

Thanks guys,
I think I'll be treating exp as itself, and if log10 or something equally horrible comes up (we dont get tables afaik, and I had no luck online), I'll just be replacing it with sin/cos and just try to get attempt marks for showing I at least know how to do second partial blah blah blah...

Thanks again.

DapperGent

What exam are you doing? Any state or college exam I've ever heard of allows you to bring in a set of log tables or provides one for you. They're about a quid from any academic bookshop or stationary shop.

DapperGent

They would look something like this:

http://www.ma.umist.ac.uk/kd/ma2m1/tables.pdf (You need Acrobat)

The derivatives section in that yoke is exactly what would be in the average log book.

One thing an average log book doesn't give (and this always annoyed me) is a rule for exponentials bigger that x.

y = exp(2x) dy/dx = (2)exp(2x)
and the integral of exp(2x) is (1/2)exp(2x)

i.e. multiplying by the power for differentiation and dividiing by it for integration.

You should definately get yourself a set of log tables though. They're like a bible.

rainbow kirby

Not allowed in UCD for exams...
So not fair.

DapperGent

rainbow kirby wrote:

Not allowed in UCD for exams...
So not fair.

That's a load of bollox. An maths exam should be about demonstrating an ability to understand and solve maths problems. Not your ****ing powers of recall.

rainbow kirby

DapperGent wrote:

That's a load of bollox. An maths exam should be about demonstrating an ability to understand and solve maths problems. Not your ****ing powers of recall.

*looks away from super-size pile of proofs for monday's exam*
you'd think UCD maths/maths physics departments would have copped onto that by now?

Syth

rainbow kirby wrote:

*looks away from super-size pile of proofs for monday's exam*
you'd think UCD maths/maths physics departments would have copped onto that by now?

Well in the maths pysics exams, the last page contains loads of useful intergration and differentation formula. Not for maths, though which is stupid.