1)(Vx-Vy)^2+(Vx+Vy)^2 = x-2Vxy+y+x+2Vxy+y=2y
2)(2Va+3Vb)^2+ (2Va+3Vb)(2Va-3Vb) = 4a+12Vab+9b+4a-9b=8a+ 12Vab
3) там что то до конца не видно!
4)(Vm-Vn)^2-(Vm-Vt) ^2- (Vn-Vt ) ^2 = m-2Vmn+m-(m-2Vmt+t)-(n-2Vnt+t)= m-2Vmn+m-m+2Vmt-t-n+2Vnt-t=m-2Vmn+2Vmt+2Vnt-2t