Comments on: Decision Maths

By: Mrs Tibble

Mrs Tibble — Sat, 22 Jan 2011 23:28:42 +0000

Hi Hannah,

When you differentiate lnx you get 1/x.
Therefore when you differentiate half lnx you get half of 1/x which is 1/(2x).
JT

By: Hannah S

Hannah S — Sat, 22 Jan 2011 21:08:34 +0000

Hi again, sorry to keep on bothering you! Probably another very easy question but how do you differentiate 1/2 lnx-2?

Thank You,
H

By: Hannah S

Hannah S — Sat, 22 Jan 2011 16:57:32 +0000

Hi! you were right (as usual) after i looked at the question again I saw the constraints thats why there was only one answer!
Have a nice weekend and you will probably be hearing from me soon!

By: Mrs Tibble

Mrs Tibble — Thu, 20 Jan 2011 21:10:47 +0000

Hi Hannah,

There are usually 2 answers for each sin cos or tan value as they are + in two and – in the other two. If there’s only one answer it must be to do with the range they have restricted the answers to. Check that out first. If it’s not that, tell me which question it is and I’ll have a look.
Mrs T

By: Hannah S

Hannah S — Thu, 20 Jan 2011 16:54:46 +0000

Thanks miss sort of get it so 60 degrees will be be pi/3 as 60 deg is 1/3 of 180? if thats right I totally understand!

Also having a bit of trouble with arcsin,cos and tan, about which quadrants to use looking in the book it is an example with

arcsin(-root2/2) thats obviously equivalent to 45 deg as its – it should go in the cos and tan quadrant but it only goes in the cos why not in the tan?

same with arctan(root3) goes in all quadrant but not tan the other positive quadrant!

Sorry bit long winded!
Thanks

By: Mrs Tibble

Mrs Tibble — Wed, 19 Jan 2011 21:29:11 +0000

Hi Hannah,

90 deg = pi/2
180 deg = pi
360 deg = 2pi

use any of these to scale up or down

eg 30 deg is one sixth of 180 so pi/6

270 deg is 3 lots of 90 so 3pi/2

Does that help or are you even more confused?!! Ask me in tomorrow’s lesson if you aren’t sure.
JT

By: Hannah S

Hannah S — Wed, 19 Jan 2011 18:01:55 +0000

Hi Mrs T,
this is C3 stuff probs really easy but how do you convert degrees into terms of pi?
I know how to convert it to radians but putting it in terms of pi i dont have a clue!

Thank You!

By: Hannah S

Hannah S — Tue, 18 Jan 2011 16:40:23 +0000

Thanks Miss, much appreciated!

By: Rachel Parkhouse

Rachel Parkhouse — Mon, 17 Jan 2011 19:43:45 +0000

I will be joining Hannah in period 3 tomorrow then! thank you.

By: Mrs Tibble

Mrs Tibble — Mon, 17 Jan 2011 19:27:17 +0000

Rachel,
I’m only free in period 3. Hannah is coming in then.