# 12-240/Classnotes for Thursday September 20

From Drorbn

Revision as of 12:33, 21 September 2012 by Dangkhoa.nguyen (Talk | contribs)

In this class, the professor completes the lecture about complex number and then introduces vector space.

## Complex number

** C**={(a,b): a, b **R**}

1 ( of **C**) = (1,0); 0 ( of **C**)= (0,0)

i=(0,1)

(a,b)+(c,d)=(a+c,b+d); (a,b)x(c,d)=(ac-bd,ad+bc)

i^2=-1

**C** contains **R** as {(a,0)} ( actually, this is not the set of real number but a copy of it )