Question

The radii of two concentric circles are $13cm$ and $8cm$. $AB$ is a diameter of the bigger circle. $BD$ is a tangent to the smaller circle touching it at $D$. Find the length $AD$.

• A. $19cm$
• B. $20cm$
• C. $25cm$
• D. $30cm$

Answer 1

The correct option is A $19cm$

We use formula,

$A{D}^2=R^2+3r^2$

where $R=13cm,r=8cm$

$\therefore A{D}^2={13}^2+3\times 8^2$

$\Rightarrow AD=\sqrt{{13}^2+3\times 8^2}$

$AD=19$cm