odd function times even function = odd function? (1 Viewer)

[underthesun]

When an odd function is multiplied by an even function, can you just say that it equals an odd function?

for example

let g(x) be an odd function, and f(x) be an even function

I{-1 --> 1}f(x)g(x) dx = 0

is it appropriate to quote it in the exam? This is because of the question 1 (ii) (c) in 1984 extension 2 paper has this thing..

 

[ND]

Why not just prove it anyway?

h(x)=f(x)*g(x) where f(x) is odd and g(x) is even.
h(-x)=f(-x)*g(-x)
=-f(x)*g(x)
=-h(x)

Doesn't take long.

 

[Newbie]

1984 exam!

you guys are scary

where did you get the paper from?

 

[ND]

I think it would be on drbuchanan's site (in the 150 past papers).

 

[ND]

Originally posted by Newbie
1984 exam!

you guys are scary

Yeh, have you already done all the papers from 02-85 underthesun?

 

[underthesun]

Originally posted by ND
Why not just prove it anyway?

h(x)=f(x)*g(x) where f(x) is odd and g(x) is even.
h(-x)=f(-x)*g(-x)
=-f(x)*g(x)
=-h(x)

Doesn't take long.

great idea mate the MANSW solution just seemed to say it straight away..

Originally posted by Newbie
1984 exam!

you guys are scary

where did you get the paper from?

If you went to last year's MANSW you'll get the "harder 3u" notes, which are very good. Probably the same with this year's, but those bludgers at my school just wagged the open day instead of getting some paper for us...

 

[underthesun]

Originally posted by ND
Yeh, have you already done all the papers from 02-85 underthesun?

naw, its just that the question was mentioned. I've only done about 1 complete 4unit paper so far. Honest!

 

[ND]

Phew, you had me worried there.

 

[freaking_out]

Originally posted by underthesun
naw, its just that the question was mentioned. I've only done about 1 complete 4unit paper so far. Honest!

what the one u sat for last year?

 

[underthesun]

Originally posted by freaking_out
what the one u sat for last year?

oh, make that two then

 

[Newbie]

how did you go last year?

 

[freaking_out]

Originally posted by Newbie
how did you go last year?

he prolly "only" got 99%....he's repeating to get 100, i think.

 

[McLake]

Just to jump in, I think it IS fair to assume odd * even = odd (again, assuming this isn't actually what the question asks)

 

[underthesun]

Originally posted by freaking_out
he prolly "only" got 99%....he's repeating to get 100, i think.

Nah, 10 marks lower than that . Yeah I was a bludger...

The only reason I'm repeating is that in 4unit I lost 5 marks due to bad rank (was in lower half of the class), and for 3unit my exam mark was 20 marks higher than the class mark.

That was a really good surprise for christmas.. really. Nearly killed myself.