My Pensieve

Prologue

I am not very good at maths. But, interesting in improving my maths knowledge and skills.
There are many people around in the same mathematical state.
This post is for them. Others might feel that I am just stating the obvious.
 I am putting two mathematical insights. First one is mine and the other is from here.

 
 Please send me the corrections diligently. :)

Epilogue:
 I was explaining this to my dad in a railway station. The guy nearby was impressed. Thought I was some math whiz (ignoring my pleadings to consider otherwise). Asked my 12th marks (my dad proudly said I got 200/200 in maths. He does not know that its harder to cross the road in Bangalore than getting good marks in public exams). Pestered my mobile number out of me (and gave me his),
 to ask "Maths" doubts. May god help him.