Rain-water harvesting is the process of collecting and storing rainwater for later use.
It is commonly done by channeling rainwater from rooftops into storage tanks or underground reservoirs.
वर्षा जल संकलन तकनीक क्या है ?
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. 
In the adjoining figure, TP and TQ are tangents drawn to a circle with centre O. If $\angle OPQ = 15^\circ$ and $\angle PTQ = \theta$, then find the value of $\sin 2\theta$. 