How to solve this binomial question?

[stiff yoke]

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[tulip elm]

okay i saw this post at first but gave up because i didnt know what c is
i know binomial expansion okay, just whats a c, i assume its not the combination symbol?

[ashen perch]

it is
nCr written as Cr

[tulip elm]

oh

[ashen perch]

n is not known in the question

[tulip elm]

what does 1+x even matter

or does this question mean for any integer n find nC0+ nC3...

[quaint spire]

$c_k$ must be the coefficient of $x^k$ in the expansion. For the first question I would fiddle with $(1+jx)^n$ and $(1+j^2x)^n$, where $j$ is a cubic root of unity, and for the second question multiply these expressions by $j$ and $j^2$