Q.
Let z1 and z2 be two distinct complex numbers and let z=(1−t)z1+tz2 for some real number t with 0<t<1. If arg(w) denotes the principal argument of a non-zero complex number w, then
2668
227
AIEEEAIEEE 2010Complex Numbers and Quadratic Equations
Report Error
Solution:
Given , z=(1−t)+t(1−t)z1+tz2
Clearly, z divides z1 and z2 in the ratio of t:(1−1),0<t<1 ⇒AP+BP+ABi.e.,∣z−z1∣+∣z−z2∣=∣z1−z2∣ ⇒ Option (a) is true.
and arg(z−z1)=arg(z2−z)=arg(z2−z1) ⇒ Option (b) is false and option (d) is true.
Also, arg(z−z1)=arg(z2−z)=arg(z2−z1) →arg(z2−z1z−z1)=0 ∴z2−z1z−z1 is purely real. ⇒z2−z1z−z1=z2−z1z−z1 or ∣∣z−z1z2−z1z−z1z2−z1∣∣=0 ∴ Option (c) is correct. Hence, (a, c, d) is the correct option.