Comments on: Pure Maths

By: Mrs Tibble

Mrs Tibble — Mon, 22 Mar 2010 20:41:56 +0000

Hi Mel,
OK. Will bring my C3 book then.
JT

Mel Cagacar — Mon, 22 Mar 2010 19:40:10 +0000

Hey Mrs Tibble
Was wondering if it’d be ok to look at some questions from C3 Ex6F tomorrow?
Thank you

Mrs Tibble — Sun, 21 Mar 2010 16:21:30 +0000

NOOOOOOOOOOOOO!
Integrate them separately.

Whenever you wonder about something like that, try putting in some numbers eg does cos75cos25 = cos90?

Megan Conway — Sun, 21 Mar 2010 16:12:13 +0000

o i get it Thankyou.
you cant add cos3x and cosx to get cos4x can you?

megan

Mrs Tibble — Sun, 21 Mar 2010 13:12:44 +0000

Hi Megan,
Have you found it?
It’s the format for the sum of two cosines.
To get the first one, add your angles; to get the second one, subtract.

Therefore 2 cos2x cosx = cos(2x+x) + cos(2x-x) = cos3x + cosx
and these are functions which you know how to integrate.
JT

Mrs Tibble — Fri, 19 Mar 2010 23:07:24 +0000

Hi Megan,

It’s one of those P+Q, P-Q thingies!
Have a look at the trig in your C3 notes for the one with the cos cos format.
Good luck

Megan Conway — Fri, 19 Mar 2010 20:39:54 +0000

i’m stuck on ex6c 3a – how do you intergrate cos2xcosx?
megan

Mrs Tibble — Wed, 17 Feb 2010 17:27:13 +0000

Find vector AB
AC is 2/3 of that
AC = c-a

I think you need to revise position vectors, in particular the general result that
vector PQ = q-p

Going out now so you’re on your own till later tonight.

DEOLA — Wed, 17 Feb 2010 17:24:19 +0000

i didnt know that produced meant extened sorry
okay i’ll try q4 again and see how it goes

yet again im stuck, i cant do part 2 of q7?

Mrs Tibble — Wed, 17 Feb 2010 17:13:38 +0000

The vectors AB and CD will be your direction vectors for finding the point of intersection. See example 33.