A chord of the larger among two concentric circles is of length 10 cm and it is tangent to the smaller circle. What is the area (in cm²) of the annular portion between the two circles?

$25\pi$

R = radius of the bigger circle

r = radius of the smaller circle

AB = 10 cm

then, AM = 5 cm

In ΔOAM , OA² = OM² + AM²

R² = r² + 5²

R² – r² = 25

We already know that,

Area between the two circle = π (R² – r²) = 25 π