Math HSC 2013 Question 16? (1 Viewer)

[TQuadded]

So I've done Questions 15 and 16 last night. All questions were pretty straight forward, except for the very last one:

http://www.boardofstudies.nsw.edu.au/hsc_exams/2013/pdf_doc/2013-hsc-maths.pdf

I believe it was Question 16 (c)(ii). I did realise the ratios, but the marking criteria asked to add them together, and I have no idea why.

 

[InteGrand]

So I've done Questions 15 and 16 last night. All questions were pretty straight forward, except for the very last one:

http://www.boardofstudies.nsw.edu.au/hsc_exams/2013/pdf_doc/2013-hsc-maths.pdf

I believe it was Question 16 (c)(ii). I did realise the ratios, but the marking criteria asked to add them together, and I have no idea why.

The marking criteria just says you need this for 2 marks: ''Correct proof''.

 

[TQuadded]

The marking criteria just says you need this for 2 marks: ''Correct proof''.

I mean I did not understand why they added the two identities together.

 

[InteGrand]

I mean I did not understand why they added the two identities together.

 

[TQuadded]

How would one even think of doing that? Maybe doing the "Prove that ...=..." in reverse?

 

[TQuadded]

Also, in the 2012 exam paper, I don't understand how it went from the third line of the solution to the fourth line in Question 15 (c)(iii).

http://www.boardofstudies.nsw.edu.a...pdf_doc/mathematics-hsc-sample-answers-12.pdf

 

[keepLooking]

Third line, he expanded the 463900(1.005^n - 1 )

 

[InteGrand]

How would one even think of doing that? Maybe doing the "Prove that ...=..." in reverse?

Basically, you should try doing as much as possible to somehow come up with expressions involved in the RTP statement. In other words, work towards what you're trying to prove, and then everything should hopefully fall out. So they added those things together as they knew that'd get them one of the sides of the equality you need to prove, so they just needed the other side of their expression to match up with the other side of the expression in the RTP statement, which it indeed did, and so the proof was complete.

 

[keepLooking]

Basically, you should try doing as much as possible to somehow come up with expressions involved in the RTP statement. In other words, work towards what you're trying to prove, and then everything should hopefully fall out. So they added those things together as they knew that'd get them one of the sides of the equality you need to prove, so they just needed the other side of their expression to match up with the other side of the expression in the RTP statement, which it indeed did, and so the proof was complete.

So I am guessing, generally there are no special 'shortcuts' to the Q16's with "complicated" RTPs?

 

[InteGrand]

So I am guessing, generally there are no special 'shortcuts' to the Q16's with "complicated" RTPs?

In general, there's no fixed way to go about tricky proofs. Sometimes you just need to try a lot of things until something works. It's usually a good idea to get the expressions in the RTP statement involved, since you're trying to prove something about them.

 

[keepLooking]

In general, there's no fixed way to go about tricky proofs. Sometimes you just need to try a lot of things until something works. It's usually a good idea to get the expressions in the RTP statement involved, since you're trying to prove something about them.

I'll keep that in mind for this afternoon. Hopefully there isn't anything too difficult.