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The minimum number of colours required to colour the vertices of a cycle with $n$ nodes in such a way that no two adjacent nodes have the same colour is

1. $2$
2. $3$
3. $4$
4. $n-2 \left \lfloor \frac{n}{2} \right \rfloor+2$
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plz someone explain clearly.....
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Thanx @Pragy Agarwal Chromatic number will be $3$ for when $n$ is odd and will be $2$ when $n$ is even. Option (D) is a representation for this, hence the correct answer

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I know that Chromatic number will be 3  when n is odd and will be 2 when n is even. But how both of them together give option D. How I will deduce that expression.
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@Gupta731 just substitute n = 3 and n = 4 in given equation. You will get the desired answer.

–1 vote
Dont u think option D is giving answer 2 only!! Bcoz 2(n/2) will give n as ans only..so n-n+2 =2??
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$2 \left \lfloor \dfrac n2 \right \rfloor = \begin{cases}n & \text{iff$n$is even}\\n-1 & \text{iff$n$is odd}\end{cases}$

So, $n - 2 \left \lfloor \dfrac n2 \right \rfloor = \begin{cases}0 & \text{iff$n$is even}\\1 & \text{iff$n$is odd}\end{cases}$

PS: The question has a typo. It says $\left [\dfrac n2 \right ]$ instead of $\left \lfloor \dfrac n2 \right \rfloor$. Let me fix it. :)
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Got it..thnx :)

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