can you multiplt by infinitie

Infinity is NOT an irrational number.

It is not a number at all.

It is a concept.   

You can multiply a number by some expression that is tending to infinity.  

If the number is pos the answer will be +infinity

If the number is negative the answer will be - infinity 

no you cant

Technically it still would just be infinite.

Infinity is an irrational number and so can not be quantified.