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Question

Mathematics Question on Algebra of Complex Numbers

Reflection of the line aˉz\bar{a}z+azˉa\bar{z}=0 in the real axis is given by

A

az+azˉ=0az+\bar{az}=0

B

aˉzazˉ=0\bar{a}z-a\bar{z}=0

C

azazˉ=0az-\bar{az}=0

D

az+aˉz=0\frac{a}{z}+\frac{\bar a}{z}=0

Answer

az+azˉ=0az+\bar{az}=0

Explanation

Solution

The correct answer is option (A): a zz+a zˉ\bar z=0

let a=α+iβa=\alpha+i\beta

z=x+iyz=x+iy

Now, aˉz+azˉ=0\bar{a}z+a \bar{z}=0

(αiβ)(x+iy)+(α+iβ)(xiy)=0\Rightarrow (\alpha-i\beta)(x+iy)+(\alpha+i\beta)(x-iy)=0

slope=αxβ-\frac{\alpha x}{\beta}

So, reflection slope = αβx\frac{\alpha}{\beta }x

Line is αxβy=0\alpha x-\beta y=0\rightarrowreflection also passes through origin

(a+aˉ2)(z+zˉ2)(aaˉ2i)(zzˉ2i)=0\Rightarrow (\frac{a+\bar{a}}{2})(\frac{z+\bar z}{2})-(\frac{a-\bar a}{2i})(\frac{z-\bar z}{2i})=0

az+azˉ=0\Rightarrow az+\bar{az}=0