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If $$z \neq 1$$ and $$\frac{z^2}{z-1}$$ is real, then the point represented by the complex number $$z$$ lies
Let $$z = x + iy$$, where $$x, y \in \mathbb{R}$$ and $$y \neq 0$$ is allowed (but $$z \neq 1$$ means $$(x,y) \neq (1,0)$$).
The given expression is $$\dfrac{z^{2}}{z-1}$$. First find the numerator and denominator in Cartesian form:
$$z^{2} = (x + iy)^{2} = (x^{2} - y^{2}) + 2ixy$$
$$z - 1 = (x - 1) + iy$$
To check when the quotient is real, multiply numerator and denominator by the conjugate of the denominator:
$$\dfrac{z^{2}}{z-1} = \dfrac{\bigl[(x^{2}-y^{2}) + 2ixy\bigr]\bigl[(x-1) - iy\bigr]}{(x-1)^{2} + y^{2}}$$
The denominator $$(x-1)^{2}+y^{2}$$ is positive (because $$z \neq 1$$), so the quotient is real exactly when the numerator is real, i.e. its imaginary part is zero.
Compute the imaginary part of the numerator:
Numerator = $$[(x^{2}-y^{2}) + 2ixy]\,[\,(x-1) - iy\,]$$
Separate real and imaginary components:
Real part: $$ (x^{2}-y^{2})(x-1) + 2xy^{2} $$
Imaginary part: $$ i\Bigl[-(x^{2}-y^{2})y + 2xy(x-1)\Bigr] $$
For the fraction to be real, the imaginary part must vanish:
$$-(x^{2}-y^{2})y + 2xy(x-1) = 0$$
Factor out $$y$$:
$$y\Bigl[-(x^{2}-y^{2}) + 2x(x-1)\Bigr] = 0$$
Case 1: $$y = 0$$Then $$z = x + i\cdot 0$$ lies on the real axis.
Case 2: $$-(x^{2}-y^{2}) + 2x(x-1) = 0$$Simplify:
$$-x^{2} + y^{2} + 2x^{2} - 2x = 0$$
$$x^{2} + y^{2} - 2x = 0$$
Complete the square in $$x$$:
$$(x^{2} - 2x + 1) + y^{2} = 1$$
$$(x - 1)^{2} + y^{2} = 1$$
This is the equation of a circle with centre at $$(1,0)$$ and radius $$1$$. Since the distance from the centre to the origin is also $$1$$, the circle passes through the origin.
Hence, the point corresponding to $$z$$ lies either on the real axis or on the circle $$(x - 1)^{2} + y^{2} = 1$$, which indeed passes through the origin.
Therefore, the correct choice is:
Option A which is: either on the real axis or on a circle passing through the origin.
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