1.

Show that the equaton of any circle in the complex plane is of the form z barz+b bar z+ b bar z+c=0,( b in C, c in R)

Answer»

Solution :Assume the genral FRORM of the equation of a circle in cartesion co-ordinates as
`x^(2)+y^(2)2ag+2fy+c=0`
`(g , f in R)""..(1)`
To write this equation in the complex VARIABLE formlet `(x,y)=Z`
Then `(z+ BAR z)/(2)= x, (z- bar z)/(2 i)`
`=y=(-i (z bar z))/(2)`
`:.x^(2)+y^(2)=|z|^(2)=z barz`
Substituting these,RESULTING in equation (1), we obtain
`z bar z+g(z+barz)+f(z- barz)(-i)+c=0`
i.e., `z bar z+(g- if)z+ (g+ if) bar z+c=0 "" (2)`
If `(g+if)=b` , then equation (2) can be writenas `z bar z+ bar b z+b bar z+c=0`


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