We
have,
${{\left(
x-a \right)}^{2}}+{{\left( y-b \right)}^{2}}={{c}^{2}}$
${{S} _{1}}\equiv
{{x}^{2}}+{{a}^{2}}-2ax+{{y}^{2}}+{{b}^{2}}-2by-{{c}^{2}}=0$
…….. (1)
${{\left(
x-b \right)}^{2}}+{{\left( y-a \right)}^{2}}={{c}^{2}}$
${{S} _{2}}\equiv
{{x}^{2}}+{{b}^{2}}-2bx+{{y}^{2}}+{{a}^{2}}-2ay-{{c}^{2}}=0$
………
(2)
Since,
$a\ne b$
Centre
of the circle ${{S} _{1}}=\left( a,b \right)$ and radius ${{r} _{1}}=c$.
We know
that the equation of common chord is ${{S} _{1}}-{{S} _{2}}=0$
So, the
equation is
$\left(
b-a \right)x+\left( a-b \right)y=0$
……..
(3)
We know
that the length of common chord is
$=2\sqrt{{{r} _{1}}^{2}-{{d} _{1}}^{2}}$
……….
(4)
Where ${{r} _{1}}=$
radius and ${{d} _{1}}$ is the length of perpendicular drawn from the
centre to the chord.
So,
${{d} _{1}}=\left|
\dfrac{\left( b-a \right)a+\left( a-b \right)b}{\sqrt{{{\left( b-a
\right)}^{2}}+{{\left( a-b \right)}^{2}}}} \right|$
$ {{d} _{1}}=\left|
\dfrac{ab-{{a}^{2}}+ab-{{b}^{2}}}{\sqrt{{{\left( a-b \right)}^{2}}+{{\left( a-b
\right)}^{2}}}} \right| $
$ {{d} _{1}}=\left|
\dfrac{2ab-{{a}^{2}}-{{b}^{2}}}{\sqrt{2{{\left( a-b \right)}^{2}}}} \right| $
$ {{d} _{1}}=\left|
\dfrac{-{{\left( a-b \right)}^{2}}}{\sqrt{2{{\left( a-b \right)}^{2}}}} \right|
$
$ {{d} _{1}}=\left|
\dfrac{-\left( a-b \right)}{\sqrt{2}} \right| $
$ {{d} _{1}}=\dfrac{\left( a-b
\right)}{\sqrt{2}} $
From equation (4),
The length of common
chord $ =2\sqrt{{{c}^{2}}-{{\left( \dfrac{a-b}{\sqrt{2}} \right)}^{2}}}
$
$
=2\sqrt{{{c}^{2}}-{{\dfrac{\left( a-b \right)}{2}}^{2}}} $
$
=2\sqrt{{{\dfrac{2{{c}^{2}}-\left( a-b \right)}{2}}^{2}}} $
$
=\sqrt{{{\dfrac{8{{c}^{2}}-4\left( a-b \right)}{2}}^{2}}} $
$
=\sqrt{4{{c}^{2}}-2{{\left( a-b \right)}^{2}}} $
Hence,
this is the answer.