Q48 / 160 · TS EAMCET 2020 (09 Sep Shift 1) · Mathematics

If A=z=x+iy/real part of z¯-1z-i=2 then the locus of the point Px,y in the Cartesian plane is

  • Correct answer
    A
    a pair of lines passing through -1,1
  • B
    a circle of radius 12 and the centre -12,32
  • C
    a pair of lines passing through -1,-2
  • D
    a circle of radius 12

Solution

Given that

Real part of z¯-1z-i = 2

here z = x+iy

⇒z¯ = x-iy

⇒z¯-1z-i = x-iy-1x+iy-i= x-1-iyx+iy-1

⇒z ¯-1z-i = x-1-iy ×x-iy-1x2+y-12

⇒z ¯-1z-i = x2-x-y-y2-ixy-x-y+1+xyx2+y-12

Real part=2

⇒x2-x+y-y2=2 x2+1+y2-2y

⇒x2+3y2+x-5y+2=0

The above represents a pair of straight lines passing through -1,1.

 

 

Hence, the correct answer is option: 'A'.

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