Multiple choice

If $\theta$ is angle of intersection of two circles of radii $a, b$ respectively then the length of common chord of two circles is

$2ab/\left( \sqrt { a^{ { 2 } }+b^{ { 2 } }-2ab\cos \theta } \right) $
$2 a b \sin \theta / \left( \sqrt { a ^ { 2 } + b ^ { 2 } + 2 a b \cos \theta } \right)$
$ab/\left( \sqrt { a^{ { 2 } }+b^{ { 2 } }-2ab\cos \theta } \right) $
N.O.T.A

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