Complex Numbers 3 Question 12

12. Let z1=10+6i and z2=4+6i. If z is any complex number such that the argument of (zz1)/(zz2) is π/4, then prove that |z79i|=32.

(1991, 4M)

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Solution:

  1. Since, z1=10+6i,z2=4+6i

and arg zz1zz2=π4 represents locus of z is a circle shown as from the figure whose centre is (7,y) and AOB=90, clearly OC=9OD=6+3=9

Centre =(7,9) and radius =62=32

Equation of circle is |z(7+9i)|=32



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