Engineering
Mathematics
Geometry of Complex Number
Question

Let  s, t, r  be non-zero complex numbers and  L  be the set of solutions  z = x + iy (x, y ∈ R, i = −1) of he equation  sz + tz¯+ r = 0 where z¯ = x – iy. Then which of the following statement(s) is(are) TRUE?

If L has more than one element, then L has infinitely many elements

If L has exactly one element, then | s | ≠ | t |

The number of elements in L ∩ {z : | z – 1 + i | = 5} is at most 2

If | s | = | t |, then L has infinitely many elements

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Solution

sz + tz¯+ r = 0

s¯z¯+t¯z+r¯= 0

⇒ss¯z+s¯tz¯+s¯r= 0

ts¯z¯+tt¯z+tr¯= 0

z( | s |2−| t |2 )  +s¯r−tr¯= 0

z=tr¯−s¯r| s |2−| t |2     | s | ≠ | t |