HL Maths Q

lc2010

Does anybody know if you have to use first principles when proving, the product rule, quotient rule, and sum rule or is the proof using logs sufficient?

zam

If it's been on past exam papers then looking at the marking scheme, that will tell you!

OxfordComma

I think it generally specifies that it has to be from first principles, if I remember correctly, and obviously if first principles is mentioned in the question, you've no other option but to do it that way. In any case, the proofs are done from first principles in maths textbooks so it's probably safer to just do it that way anyways.

Ruski

I'm pretty sure the two most popular, and most likely accepted methods are the lim(h->0) [f(x+h)-f(x)]/h method and the delta method. Never heard about the log method.

Michael Collins

Yes, the log method of proving both of those rules is acceptable (even though it is highly questionable from a rigourous mathematical point of view!).

They are of course not proofs from first principles, but any questions on the paper asking you to prove those rules won't ask you to prove them from first principles anymore.

Note: this only applies to the current syllabus, when the new Project Maths comes in this may change!

eoins23456

http://www.rte.ie/exams/mathsnotes/easyway.pdf

Easy way to do the product and quotient rule using the delta x method if ya want to give it a look.The log method isnt a correct method of doing it but its acceptable.

So chances of the quotient rule coming up this year?or demoivre theorem for negative numbers?