Two concentric circles are of radii $4$ cm and $3$ cm. Find the length of the chord of the larger circle which touches the smaller circle.

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Step 1: Here $OB = 3$ cm, $OA = 4$ cm. $OB \perp AC$ (radius to tangent point).
Step 2: $AB = \sqrt{OA^2 - OB^2} = \sqrt{4^2 - 3^2} = \sqrt{7}$ cm
Step 3: Hence $AC = 2\sqrt{7}$ cm

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