Need help with a riddle

[jeans]

A friend challenged me with this riddle, but I haven't figured it out yet.

12+1=2 - How is this possible?

Any ideas?

[parvez]

let a=b
a^2=ab
a^2-b^2=ab-b^2
(a+b)(a-b)=b(a-b)
a+b=b
let a=11,b=2
11+2=2
12+1=2