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C3 January 2013 25/01/2013

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Reply 1780

Jack_Smith

Original post by Skaterkid

how would you do this someone!!! what values would you put into tan(a+b)

You would use the tan2A formula so A would be 22.5

Reply 1781

posthumus

Original post by Alex_1

Has anyone been taught how to do the half angle questions? Do we need to know that for our exams? I'm really starting to panic now :erm:

Don't stress :tongue:

Its not much of a formula

the common one is just

sin2x = 2sinxcosx

1/2(sin2x) = sinxcosx

^^ half angle formula :tongue:

Reply 1782

Alex_1

Original post by MyNameIsRay

How do you differentiate these:
Sec kx
Cot kx
Cosec kx

is it:
ksec(kx)tan(kx)
-kcosec^2(kx)
-kcosec(kx)cot(kx)

(They're not on data sheet with k, only tankx is)

I have a question with y=e^(2x) sec(3x) and need to find dy/dx and not sure what to do for sec.
I know I can just make it e^(2x) / cos(3x) and use the quotient rule but I would rather learn this way ^^

Aren't the differentiation for cot sec and cosec in the formula booklet?? I think tan is also in there :-)

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Reply 1783

MyNameIsRay

Original post by Alex_1

Aren't the differentiation for cot sec and cosec in the formula booklet?? I think tan is also in there :-)

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yes but only tan has in terms of "kx"

Reply 1784

oli_G

Original post by Alex_1

Has anyone been taught how to do the half angle questions? Do we need to know that for our exams? I'm really starting to panic now :erm:

It's best to know them, although they can be worked out from the addition formulas.

sin2x=2sinxcosx

cos2x=cos^2x-sin^2x=2cos^2x-1=1-2sin^2x

tan2x=\frac{2tanx}{1-tan^2x}

Reply 1785

suncake

Original post by This Excellency

I hope so! My teacher reckons it's easier than C3 but then again, he teaches maths for a reason. :rolleyes:

New hat

Pimp hat? Rap star hat? Top hat?
I wish I could wear hats. I just look weird :tongue:

Haven't been doing any work either. I'm just watching Southland :tongue:

We still have all of tomorrow morning to do some last minute prep.

Good luck to you too :h:

You going for the A*?

My teacher says that too :lol:

I wish it was a pimp hat... But no, just a boring winter beanie/beret thing :tongue:

I look weird in hats too, hence why I faffed around with it for an hour :awesome:

Yeah, feels like I've done like 2402389 past papers this month. Not trusting myself to leave things till morning though, considering I slept in till 11am today hahah.
Yuuup I am :smile:

Actually did C3 already last summer, but aiming for a very high UMS now to take the pressure off C4!

Original post by Bulbasaur

That's a relief! :tongue:

C3 isn't exactly hard, it's just annoying.

Agree. It's all the graphs! :unimpressed:

(edited 11 years ago)

Reply 1786

Skaterkid

Original post by Jack_Smith

You would use the tan2A formula so A would be 22.5

how would I enter tan22.5 under tan^2

Reply 1787

Jack_Smith

Original post by Skaterkid

how would I enter tan22.5 under tan^2

(tan(22.5))^2

Reply 1788

Skaterkid

Original post by Jack_Smith

(tan(22.5))^2

all of that equals to 1

Reply 1789

Jack_Smith

Original post by Skaterkid

all of that equals to 1

Hope this helps:

We can prove this using the identity:
tan(2A)=2tan(A) / (1-tan^2 A)

We already know that tan 45 = 1
Let A =22.5 so that tan 2A = tan 45 = 1

tan(45)=2tan(22.5) / (1-tan^2 22.5)
1 =2tan(22.5) / (1-tan^2 22.5)
(1-tan^2 22.5) = 2tan(22.5)
(1-tan^2 22.5) = 2tan(22.5)
(tan^2 22.5) + 2tan (22.5) - 1 = 0
let tan 22.5 = x
x^2 + 2x - 1 = 0

x= -1+root 2 or -1-root 2

but we know from the tan graph that tan22.5 is positive.
tan 22.5 = -1 + root(2)

Reply 1790

Skaterkid

Original post by Jack_Smith

thanks so much

negged??

(edited 11 years ago)

Reply 1791

Mus1995

I struggle to see where domains lie has anyone got any tips on how to deduce them? And ranges?

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Reply 1792

Skaterkid

Original post by Jack_Smith

Sorry if this is getting annoying now

in the solomon papers theres 52.5 how would you work it out since you cannot make it equal to tan45 I tried to double 52.5 and tan105 didnt work :s-smilie:

Reply 1793

Jack_Smith

Original post by Skaterkid

Sorry if this is getting annoying now

in the solomon papers theres 52.5 how would you work it out since you cannot make it equal to tan45 I tried to double 52.5 and tan105 didnt work :s-smilie:

you can do tan ( 22.5 + 30) = root 3/3 :smile:

Reply 1794

Jack_Smith

Original post by Mus1995

I struggle to see where domains lie has anyone got any tips on how to deduce them? And ranges?

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i feel sketching the graph really helps :smile:

Reply 1795

Dragonrage973

Original post by Skaterkid

Sorry if this is getting annoying now

in the solomon papers theres 52.5 how would you work it out since you cannot make it equal to tan45 I tried to double 52.5 and tan105 didnt work :s-smilie: