[tex]\displaystyle\bf\\(a-4)(a+4)-(2a-1)^{2} =a^{2} -4^{2} -\Big[(2a)^{2}-2\cdot 2a\cdot 1+1^{2} \Big]=\\\\=a^{2} -16-4a^{2} +4a-1=(a^{2} -4a^{2} )+4a-(16+1)=\\\\=-3a^{2} +4a-17[/tex]