Two reagents that can be used to remove ballpoint pen stains are:
1. Rubbing alcohol – It helps dissolve ink stains from the fabric.
2. Hair spray – The alcohol content in hair spray can help break down the ink stain.
In the adjoining figure, $\triangle CAB$ is a right triangle, right angled at A and $AD \perp BC$. Prove that $\triangle ADB \sim \triangle CDA$. Further, if $BC = 10$ cm and $CD = 2$ cm, find the length of AD.