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(silly) question on de moivre's theorem expansion

Suppose I have the following complex number:

Unparseable latex formula:

\[z = \cos 4\theta + i\sin 4\theta



Using de Moivre's, I write it as:

(cosθ+isinθ)4[br][br](40)cos4θ(isinθ)0++(44)cos0θ(isinθ)4\equiv (\cos \theta + i\sin \theta )^{4} [br][br]\equiv \binom{4}{0}\cos ^{4} \theta(i\sin \theta )^{0} + \cdots + \binom{4}{4} \cos ^{0}\theta \left ( i\sin \theta \right )^{4}

Now to save the pain of writing out all the sin and cos terms in the binomial expansion step, I've written "i x sin(theta)" as "is" and "cos(theta)" as "c".

Unparseable latex formula:

\equiv \binom{4}{0}c^{4}(is)^{0}+\cdots + \binom{4}{4}c^{0}(is)^{4}\]



Now my question is, is this form allowed in examinations? I write it like this to save time but will the examiner look kindly towards it?
Reply 1
Original post by aymanzayedmannan
Suppose I have the following complex number:

Unparseable latex formula:

\[z = \cos 4\theta + i\sin 4\theta



Using de Moivre's, I write it as:

(cosθ+isinθ)4[br][br](40)cos4θ(isinθ)0++(44)cos0θ(isinθ)4\equiv (\cos \theta + i\sin \theta )^{4} [br][br]\equiv \binom{4}{0}\cos ^{4} \theta(i\sin \theta )^{0} + \cdots + \binom{4}{4} \cos ^{0}\theta \left ( i\sin \theta \right )^{4}

Now to save the pain of writing out all the sin and cos terms in the binomial expansion step, I've written "i x sin(theta)" as "is" and "cos(theta)" as "c".

Unparseable latex formula:

\equiv \binom{4}{0}c^{4}(is)^{0}+\cdots + \binom{4}{4}c^{0}(is)^{4}\]



Now my question is, is this form allowed in examinations? I write it like this to save time but will the examiner look kindly towards it?


definitely
(and if they don't I would go afterwards and smash the "shop" up ...)
Original post by aymanzayedmannan
Suppose I have the following complex number:

Unparseable latex formula:

\[z = \cos 4\theta + i\sin 4\theta



Using de Moivre's, I write it as:

(cosθ+isinθ)4[br][br](40)cos4θ(isinθ)0++(44)cos0θ(isinθ)4\equiv (\cos \theta + i\sin \theta )^{4} [br][br]\equiv \binom{4}{0}\cos ^{4} \theta(i\sin \theta )^{0} + \cdots + \binom{4}{4} \cos ^{0}\theta \left ( i\sin \theta \right )^{4}

Now to save the pain of writing out all the sin and cos terms in the binomial expansion step, I've written "i x sin(theta)" as "is" and "cos(theta)" as "c".

Unparseable latex formula:

\equiv \binom{4}{0}c^{4}(is)^{0}+\cdots + \binom{4}{4}c^{0}(is)^{4}\]



Now my question is, is this form allowed in examinations? I write it like this to save time but will the examiner look kindly towards it?


You need to write it out in full in the exam - or say where s = sin (theta) etc -
Original post by TeeEm
definitely
(and if they don't I would go afterwards and smash the "shop" up ...)


calm down dear
Reply 4
Original post by the bear
calm down dear


I had a bad teaching and my dinner is not ready...
I will be calmer once I have eaten.
Original post by aymanzayedmannan
Suppose I have the following complex number:

Unparseable latex formula:

\[z = \cos 4\theta + i\sin 4\theta



Using de Moivre's, I write it as:

(cosθ+isinθ)4[br][br](40)cos4θ(isinθ)0++(44)cos0θ(isinθ)4\equiv (\cos \theta + i\sin \theta )^{4} [br][br]\equiv \binom{4}{0}\cos ^{4} \theta(i\sin \theta )^{0} + \cdots + \binom{4}{4} \cos ^{0}\theta \left ( i\sin \theta \right )^{4}

Now to save the pain of writing out all the sin and cos terms in the binomial expansion step, I've written "i x sin(theta)" as "is" and "cos(theta)" as "c".

Unparseable latex formula:

\equiv \binom{4}{0}c^{4}(is)^{0}+\cdots + \binom{4}{4}c^{0}(is)^{4}\]



Now my question is, is this form allowed in examinations? I write it like this to save time but will the examiner look kindly towards it?
You should put a line in like: "write ss for sinθ\sin \theta, cc for cosθ\cos \theta" and then it will be fine. (I doubt you'd lose marks for not writing tihs, but it's the "right" way to do it).
Reply 6
Original post by DFranklin
You should put a line in like: "write ss for sinθ\sin \theta, cc for cosθ\cos \theta" and then it will be fine. (I doubt you'd lose marks for not writing tihs, but it's the "right" way to do it).


I guess a legend would be the safe way to go about it. Thank you!

Original post by TeeEm
definitely
(and if they don't I would go afterwards and smash the "shop" up ...)


Hahahaha made my night. I'll be booking a flight to Edexcel HQ for 13th August next year along with my cricket bat...

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