Area between the circles

Geometry Level 3

AB is 10 cm and tangent to the smaller circle. Find the area between the two concentric circles in square centimeters (use pi = 3.14)

2 solutions

A Former Brilliant Member
Oct 18, 2017

The area between the two circles is

$A=\pi R^2-\pi r^2=\pi(R^2-r^2)$

Using pythagorean theorem, we have

$R^2=r^2+5^2$

$R^2-r^2=25$

Finally,

$A=3.14(25)=$ $\boxed{78.5}$

Cleres Cupertino
Aug 21, 2015

$\pi(R^2-r^2)=3.14*25=78.5$