a) \(x^2-6x+13+t^2+4t\Leftrightarrow\left(x^2-6x+9\right)+\left(t^2+4t+4\right)\)
\(\Leftrightarrow\left(x-3\right)^2+\left(t+2\right)^2\)
b) \(4x^2+2z^2-4xz-2z+1\Leftrightarrow\left(4x^2-4xz+z^2\right)+\left(z^2-2z+1\right)\)
\(\Leftrightarrow\left(2x-z\right)^2+\left(z-1\right)^2\)