The locus of the point representing the complex number $z$ for which $|z+3|^2-|z-3|^2=15$ is
The locus of the point representing the complex number $z$ for which $|z+3|^2-|z-3|^2=15$ is
- a circle
- a parabola
- a straight line
- an ellipse
Solution
Let the comlex number, $z=x+i y$
Now, $|z+3|^2-|z-3|^2=15$
$\begin{aligned}
& \therefore \quad|x+i y+3|^2-|x+i y-3|^2=15 \\
& (x+3)^2+y^2-(x-3)^2-y^2=15 \\
& x^2+6 x+9-x^2+6 x-9=15 \\
& 12 x=15 \Rightarrow 4 x=5
\end{aligned}$
$\therefore$ It represents a straight line.
Asked in: AP EAMCET 2016
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