Complex Number Questions (1 Viewer)

[tacogym27101990]

Why the hell does the Board Of Studies use the 'cis' notation and what is it ?

its just a quicker way to write cos@ + isin@
which is just the modulus/arguement form of a complex number

 

[ronnknee]

Why the hell does the Board Of Studies use the 'cis' notation and what is it ?

cis @ is the notation for cos @ + isin @
It saves time and space writing it I guess xD

 

[Forbidden.]

its just a quicker way to write cos@ + isin@
which is just the modulus/arguement form of a complex number

cis θ = cosθ + i sin θ ?
Nah, sometimes I just prefer e^iθ or the long way cosθ + i sin θ,
cis θ looks to confusing and impractical to me anyway.

and LOl at your sig ... sometimes fat physics textbook make bedtime story too.

 

[Undermyskin]

I always write cis but I'm not sure if I can do it in the HSC exam. (?)

 

[conics2008]

ohh that lol.. hehe i thoguht u meant this cos2x lol this is 3unit xD

this is what i thought

sina+sinb= 2sin(a+b/2)cos(a-b/2)

because they used it in the cambridge book to prove the gradient of a line in an ellipes...

ahhaha.. sorry im gettin too old for this shit.

 

[conics2008]

ohh that lol.. hehe i thoguht u meant this cos2x lol this is 3unit xD

this is what i thought

sina+sinb= 2sin(a+b/2)cos(a-b/2)

because they used it in the cambridge book to prove the gradient of a line in an ellipes...

ahhaha.. sorry im gettin too old for this shit.

 

[tacogym27101990]

yeah im pretty sure you can
its part of the syllabus i think

 

[conics2008]

I use that form cis theta

c= cos theta
i = i
s= sin theta

theta=theta

 

[conics2008]

there are these half angels

sin(x) = 2sinx/2cosx/2
cos(x) = cos^2(x/2)-sin^2(x/2)
= 2cos^2(x/2) -1

tan(x) = 2tanx/2 / 1 - tan^2 x/2

these im postive and the other i posted is not in the syllabus

 

[tacogym27101990]

yeah they are
its just a different form of the cos2x and stuff
u just let sinx=sin(x/2+x/2)
then use the result we know of sin(A+B)=sinAcosB+cosAsinB
to get 2sinx/2cosx/2
and cos(A+B) is cosAcosB-sinAsinB
and i cant be bothered doin the tan one

 

[conics2008]

yeah they are
its just a different form of the cos2x and stuff
u just let sinx=sin(x/2+x/2)
then use the result we know of sin(A+B)=sinAcosB+cosAsinB
to get 2sinx/2cosx/2
and cos(A+B) is cosAcosB-sinAsinB
and i cant be bothered doin the tan one

Cool thanks =) HSC question aren't that hard except for 7 and 8 ... im confident i can get 1st 2nd 3rd and 4th.. full marks... unless i make stupid mistakes along the way.

 

[ronnknee]

Cool thanks =) HSC question aren't that hard except for 7 and 8 ... im confident i can get 1st 2nd 3rd and 4th.. full marks... unless i make stupid mistakes along the way.

It's so relevant :|

 

[tacogym27101990]

It's so relevant :|

haha yeah i think he does it in like all posts