Mathematics · Complex Numbers

JEE Main 2025 — 3 April, Evening Shift — Question 37

If z1,z2,z3∈Cz_{1}, z_{2}, z_{3} \in \mathbb{C} are the vertices of an equilateral triangle, whose centroid is z0z_{0}, then ∑k=13(zk−z0)2\sum_{k=1}^{3}\left(z_{k}-z_{0}\right)^{2}

is equal to

  1. Option A:

    0

    Correct
  2. Option B:

    1

  3. Option C:

    ii

  4. Option D:

    −i-i

Answer: A

Step-by-step solution

Z0=Z1+Z2+Z3Z_{0}=Z_{1}+Z_{2}+Z_{3}

∑k=13(zk−z0)2=(z1−z0)2+(z2−z0)2+(z3−z0)2\sum_{k=1}^{3}\left(z_{k}-z_{0}\right)^{2}=\left(z_{1}-z_{0}\right)^{2}+\left(z_{2}-z_{0}\right)^{2}+\left(z_{3}-z_{0}\right)^{2}

Let z0z_{0} is origin ⇒z1,z2,z3\Rightarrow z_{1}, z_{2}, z_{3} lies on a circle

 having ∣z0−zi∣=R\text { having }\left|z_{0}-z_{i}\right|=R

∴z1=Rei2π/3Z2=Rei4π/3z3=Reiσπ/3\therefore z_{1}=R e^{i 2 \pi / 3} Z_{2}=R e^{i 4 \pi / 3} z_{3}=R e^{i \sigma \pi / 3}

⇒z12+z22+z32=R2[ei4π/3+ei8π/3+ei12π/3]\Rightarrow z_{1}^{2}+z_{2}^{2}+z_{3}^{2}=R^{2}\left[e^{i 4 \pi / 3}+e^{i 8 \pi / 3}+e^{i 12 \pi / 3}\right]

=0=0

∴∑k=13(zk−z0)2=0\therefore \sum_{k=1}^{3}\left(z_{k}-z_{0}\right)^{2}=0

Solution figure

Answer key and solution verified before publishing.

Practise Complex Numbers

Start with this question, then two more from the same chapter — with a tutor that explains every step. Free.

Exam
JEE Main 2025
Subject
Mathematics
Chapter
Complex Numbers
Topic
Geometry of Complex Numbers