The expression can be simplified using trigonometric identities:

cos^2a - 2cosacosb + cos^2b + sin^2a - 2sinasinb + sin^2b
= (cos^2a + sin^2a) - 2cosacosb - 2sinasinb + (cos^2b + sin^2b)
= 1 - 2cosacosb - 2sinasinb + 1
= 2 - 2(cosacosb + sinasinb)
= 2 - 2(cos(a)cos(b) + sin(a)sin(b))
= 2 - 2cos(a-b)
= 2 - 2cos^2(0)
= 2 - 2(1)
= 0

Therefore, the simplified expression is 0.