Quicks maths question (1 Viewer)

[PROFESSOROAK]

Hey, In my ext 1 maths exam, there was this question

y = lnx / e ^-x
derive it.

and i simplified and derived it like the image and i lost the 2 marks for it =/ I know you can factorise it but still thats not neccessary, did i do something wrong

http://img689.imageshack.us/i/75480471.jpg/

 

[Drongoski]

Yr soln looks ok to me except maybe u could have "simplified" it to:

e^x [1/x + ln x]

but you should at least get > 50% of total mark allocated.

 

[PROFESSOROAK]

how important is factorising it? I derived it, wouldn't that be enough?

 

[jet]

Differentiated, not derived!

Deriving is where you logically obtain something (like an equation) from other principles. Not the same thing.

 

[Dx_God]

can u give out the full question so i can see whether u can actually use differentiation, and alot of times u have to give reasons (not necessary to be in words) to why u did this as it is part of the process of deriving. without doing so, the marker can say that u might have made up bs and got the answer without actually knowing the concept behind it.

 

[PROFESSOROAK]

It was just y = lnx / e ^-x, and differentiate it. Everyone used quotient rule, but I find that method retarded, why not make it more simplier and just simplify it to e^x.lnx then use product? AND THE QUESTION DID NOT SAY USE QUOTIENT RULE.

 

[jet]

Quotient rule is the product rule in disguise.