# If the reflection of the line $\bar{a}z + a \bar{z}= 0$ in the real axis is $\bar{\alpha}z + \alpha \bar{z}= 0$ in the simplest form

Q: If the reflection of the line $\bar{a}z + a \bar{z}= 0$ in the real axis is $\bar{\alpha}z + \alpha \bar{z}= 0$ in the simplest form, then

(A) α + a is purely real

(B) $\bar{\alpha} – a$ is purely real

(C) $\alpha -\bar{a}$ is purely real

(D) $\bar{\alpha} -\bar{a}$ is purely imaginary

Ans: (B) & (C)
Sol: Let a = a1 + ia2 and z = x + iy, then

$\bar{a}z + a \bar{z}= 0$

⇒ a1 x + a2 y = 0

or , $\large y = (-\frac{a_1}{a_2})x$

Its reflection in the real axis (x-axis) is $\large y = (\frac{a_1}{a_2})x$

or, a1 x – a2 y = 0

i.e. $\large (\frac{a + \bar{a}}{2}) (\frac{z + \bar{z}}{2}) – (\frac{a – \bar{a}}{2i}) (\frac{z – \bar{z}}{2i})= 0$

So, $\large \bar{\alpha} = a$ and $\large \alpha = \bar{a}$

Hence (B) and (C) are the correct answers.