[tex]\displaystyle\bf\\1)\\\\\frac{a+7}{a-7} -\frac{a-7}{a+7} =\frac{(a+7)^{2} -(a-7)^{2} }{(a-7)(a+7)} =\frac{(a+7+a-7)(a+7-a+7)}{(a-7)(a+7)} =\\\\\\=\frac{2a\cdot14}{(a-7)(a+7)} =\frac{28a}{(a-7)(a+7)} \\\\2)\\\\\frac{28a}{(a-7)(a+7)}:\frac{19}{a^{2} -7a} =\frac{28a}{(a-7)(a+7)}\cdot\frac{a\cdot(a-7)}{19} =\frac{28a^{2} }{19(a+7)}[/tex]