Proving trig identities (1 Viewer)

[sl3epyAZN]

I got this question in my ext 2 half yearlies, the teacher gave me 2/3 because she said the proof is informal. However, according to my private tutor, he said that in HSC i would get full marks. I would like to know the opinions of you guys.

The question was from Ext 1 1990 past paper.

All my workings are right. Format is the problem here.

 

[Mill]

If you wrote "RTP:" before your restatement of what you are trying to prove then that would be correct. You did not.

Without it, you are technically making a statement that has obvously not yet been proved.

In the HSC, you would probably not be penalised for such a mistake.

But if your teacher wants to penalise you for that then I think he has every right.

 

[sl3epyAZN]

what does RTP mean?

 

[idling fire]

what does RTP mean?

Required to prove. (or remains... whatever takes your fancy)

 

[sl3epyAZN]

If you wrote "RTP:" before your restatement of what you are trying to prove then that would be correct. You did not.

Without it, you are technically making a statement that has obvously not yet been proved.

In the HSC, you would probably not be penalised for such a mistake.

But if your teacher wants to penalise you for that then I think he has every right.

I did not make a statement, i merely changed the layout of a given statement. The layout of a statement does not change the statement at all. Even if the given statement is not true, you still can change the layout of the statement.

It is just like changing
aX²+bX=-C
to
aX²+bX+C=0
to
aX²+bX+D=E

Also,
If it is right to prove a questions by using LHS-RHS=0,
why cant you prove LHS - part of RHS = reminder of RHS?

 

[ellen.louise]

I dont think you can do that cause you don't know that its true to start with.
You could argue your point with your teacher, but in the end it's only one mark, which is worth a tiny percentage towards your HSC. Really, teachers can take marks off for whatever, and if they can see something wrong with your proof, and it was a standard thing that everyone would have lost marks for, there's not much you can do. Sort of like when you do a circle geometry proof and you incorrectly name the property you used. You lose marks.

 

[sl3epyAZN]

is there a way to ask the proper Board of studies about this?
I seriously think there is nothing wrong with my way of proving, and teachers should mark to HSC standards for math and science subjects. Im unsure of the HSC standards are, different people being telling me different things.

 

[pLuvia]

Your working assumes that, that identity exists, except you are suppose to show that it exists. In the HSC you wouldn't get full marks for that either

You can try emailing the BOS or calling them

 

[ellen.louise]

pretty sure pLuvia's right, man. Let it go.

 

[Mill]

The question says:

RTP: A = B - C.

It is perfectly reasonable to restate the question and say:

RTP: A - B = - C

These are EQUIVALENT questions or proofs.


HOWEVER you wrote the equation:


A - B = - C

WITHOUT WRITING "RTP:" BEFORE IT

and then commenced your working.

as subtle as it may be, by not putting "RTP:" before that equation, you are in effect MAKING IT A STATEMENT as opposed to a PROPOSITION which you still wish to PROVE.




like i said, an hsc marker won't care, but it looks like your teacher does. i would have given you 2/3 if i was marking it too.