Radii of two concentric circles are 40 cm and 41 cm. AB is a chord of the bigger circle and tangent to the smaller circle. Find the length of AB
OC=40cm,OB=41cm
OC⊥AB since AB is tangent to the smaller circle .
⟹AC+BC
In △OCB
OB2=OC2+BC2
⟹BC2=412–402=818×1
⟹BC=9cm
⟹AB=2BC=18cm