\[\boxed{\text{715\ (715).\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[1)\ a^{7} + ab^{6} = a\left( a^{6} + b^{6} \right) =\]
\[= a(a^{2} + b^{2})(a^{4} - a^{2}b^{2} + b^{4})\]
\[2)\ x^{8} - y^{8} =\]
\[= \left( x^{4} - y^{4} \right)\left( x^{4} + y^{4} \right) =\]
\[= \left( x^{2} - y^{2} \right)\left( x^{2} + y^{2} \right)\left( x^{4} + y^{4} \right) =\]
\[= (x - y)(x + y)\left( x^{2} + y^{2} \right)\left( x^{4} + y^{4} \right)\]
\[3)\ c^{6} - 1 = \left( c^{3} - 1 \right)\left( c^{3} + 1 \right) =\]