a,\(x^2-2xy+2y^2+2y+1=\left(x^2-2xy+y^2\right)+\left(y^2+2y+1\right)=\left(x-y\right)^2+\left(y+1\right)^2\)
b,\(4x^2-4x+y^2+2y+2=\left(4x^2-4x+1\right)+\left(y^2+2y+1\right)=\left(2x-1\right)^2+\left(y+1\right)^2\)
c, \(z^2-6z+5-t^2-4t=\left(z^2-6z+9\right)-\left(t^2-4t+4\right)=\left(z-9\right)^2-\left(t-2\right)^2\)