1. Mar 23, 2012

### datdere

I don't know if this is calculus or not but this was on a calculus test. It was the last step of a third derivative question. I lost a mark because the teacher says (x^2-1)/x^2 is more simplified than 1-(1/x^2).. is this fair? Is there an official rule that states (x^2-1)/x^2 is more simplified? Normally I wouldn't care about one mark but I was getting 100 in the course and that section was only out of 8 so now my mark is going to plummet for no reason.. -_-

2. Mar 23, 2012

### chrisbaird

I take off points for my students if they don't combine fractions like this, and they also complain. Fair? That is in the eye of the beholder. Usually when you combine fractions by putting them over a common denominator, the numerator simplifies quite a bit. For example, sqrt(1/16 + 1/9) reduces to 5/12.

3. Mar 23, 2012

### mtayab1994

Well it is more simplified because you have to simplify it by finding the common denominator, therefore your teacher is correct. By the way it's nothing serious so don't be hard on yourself.

4. Mar 23, 2012

### xaos

technicality. no way to get out of it. file it under 'syntax deduction'. perhaps attention to detail is required but not always necessary.

5. Mar 23, 2012

### Staff: Mentor

IMO, and having worked as a college math teacher for 19 years, I would say that the teacher is being pedantic and arbitrary in saying that his/her form is simpler than yours. Arguments could be made for either form being advantageous, but if you had to take one more derivative (the 4th), your form would be much simpler to work with. I'm assuming that the problem instructions didn't specify the form in which the answer should appear. If there were no such instructions, I don't understand why your teacher felt the need to deduct a point.

6. Mar 23, 2012

### datdere

you forgot the part where the fraction here DOESNT become simplified when you combine the fraction.. in fact it becomes complified therefore i don't see a reason to do this. there was another question where taking the common denom cancelled out some stuff but here it did nothing so i didn't do it..

7. Mar 23, 2012

### Curious3141

Exactly right. I don't agree with the teacher.

For that matter, what if I'd "simplified" the expression further by a needless factorisation to (x+1)(x-1)/x^2? Would I get extra credit?

8. Mar 23, 2012

### datdere

Thanks for the replies, any more thoughts so I can show him this thread? If there's no official rule about making a common denominator I'm going to talk to her about this again (I tried once already T.T).

The only solid thing I can say is that taking the derivative of my form is easier, and since he said always use a simplified form before taking the next derivative, his argument is in my favour, lol

Honestly if there's no written rules about this it doesn't make sense to take off a whole mark out of 3 -.-

also want to add @chrisbaird, why are you taking marks off from your students when it's clearly a debatable topic? If you have students arguing about it, why are you taking off marks? I don't understand.

Last edited: Mar 23, 2012
9. Mar 27, 2012

### chrisbaird

Your case does not seem as serious a mistake as others, but when you get into other topics such as infinite series expansions, taking this step becomes crucial.