posted by manisha .
In "Principia Mathematica", Alfred North Whitehead and Bertrand Russell succeed in proving that 1+1=2 on page 379 of Volume 1. I would imagine the proof of the above proposition can be found somewhere between the start of the book and page 378.
The quantity on one side of an equals sign is identical to the quantity on the other side.
= means that 1 is equal to 1 (suppose that there is X and its given that X=5 , so the value of X is equal to 5)