[tex]\displaystyle\bf\\1,21p^{2} -a^{6} =(1,1p)^{2} -(a^{3} )^{2}=(1,1p-a^{3} )(1,1p+a^{3}) \\\\\\9y^{6} -4a^{4} =(3y^{3} )^{2} -(2a^{2} )^{2}=(3y^{3} -2a^{2} )(3y^{3} +2a^{2})\\\\\\0,81a^{4} -0,49b^{6} =(0,9a^{2} )^{2} -(0,7b^{3} )^{2}=(0,9a^{2} -0,7b^{3} )(0,9a^{2} +0,7b^{3})\\\\\\0,01x^{16} -0,16 =(0,1x^{8} )^{2} -(0,4 )^{2}=(0,1x^{8} -0,4)(0,1x^{8} +0,4)[/tex]

[tex]\displaystyle\bf\\\frac{4}{9} m^{6} -\frac{25}{36} =\Big(\frac{2}{3}m^{3}\Big)^{2} -\Big(\frac{5}{6}\Big )^{2}=\Big(\frac{2}{3} m^{3} -\frac{5}{6} \Big )\Big(\frac{2}{3} m^{3} +\frac{5}{6} \Big)[/tex]