[tex]\displaystyle\bf\\\Big(t^2-z^2\Big)^2=\\\\=\Big(t^2\Big)^2-2t^2z^2+\Big(z^2\Big)^2=\\\\=t^{2\times2}-2t^2z^2+z^{2\times2}=\\\\=\boxed{\bf t^{4}-2t^2z^2+z^{4}}[/tex]
