Q.
If z1 and z2 are two non-zero complex numbers such that ∣z1+z2∣=∣z1∣+∣z2∣, then arg (z2z1) is equal to
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Complex Numbers and Quadratic Equations
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Solution:
Given ∣z1+z2∣=∣z1∣+∣z2∣
We know that ∣z1+z2∣≤∣z1∣+∣z2∣
Equality holds when z1, z2 are collinear with the origin. ⇒arg(z2z1)=argz1−argz2=0