(1)m²+2n-mn-2m
=m²-mn+2n-2m
=m(m-n)-2(m-n)
=(m-n)(m-2)
(2)a²-4a+4-c²
=(a²-4a+4)-c²
=(a-2)²-c²
=(a-2+c)(a-2-c)