А) (a+1)^2-2(a+1)+1= а^2+2a+1-2a-2+1=a^2
б) (m-n)^2+2n(m-n)+n^2 = m^2-2mn+n^2+2nm-2n^2+n^2=m^2
в) (t-s)^2-2(t^2-s^2)+(t+s)^2=t^2-2ts+s^2-2t^2+2s^2+t^2+2ts+s^2=4s^2
г) a(a-b)+b(a+b)+(a-b)(a+b)=a^2-ab+ba+b^2+a^2-b^2=2a^
д) (c-d)^2-(c+d)(d-c)+2cd=c^2-2cd+d^2+c^2-d^2+2cd=2c^2