A magnifying glass can be utilized to focus sunlight to a single point. Describe physically and mathematically how this process occurs using:
a) Geometrical ray optics
[Hint: the sunlight can be considered as an object located at infinity]
b) Image formation by lens
[Hint: the sunlight can be mathematically expressed as source of infinite extent, of constant light intensity, given by f(x, y)=a where a is a constant]