Let O be the centre of the concentric circles and AB is the chord of the larger circle and touches the circle with the smaller radius at M. OA=radius of the greater circle=73 OM=radius of the smaller circle=55 Also OM⊥AB (AB is the tangent for smaller circle) In △OMA, ∠OMA=90° OA²=OM²+MA² ⇒MA²=OA²-OM²=(73)²-(55)²=(73+55)(73-55)=(128)(18)=(48)² ∴MA=48 ∴AB=2MA=2(48)=96 Thus, the length of the chord is 96.