\[\boxed{\text{1025.}\text{\ }еуроки - ответы\ на\ пятёрку}\]
\[\textbf{а)}\ 9c^{15} - c^{13} = c^{13} \cdot\]
\[\cdot \left( 9c^{2} - 1 \right) = c^{13} \cdot\]
\[\cdot (3c - 1)(3c + 1)\]
\[\textbf{б)}\ x^{22} - \frac{1}{49}x^{20} = x^{20} \cdot\]
\[\cdot \left( x^{2} - \frac{1}{49} \right) = x^{20} \cdot\]
\[\cdot \left( x - \frac{1}{7} \right)\left( x + \frac{1}{7} \right)\]
\[\textbf{в)}\ a^{5} - 0,64a^{2} = a²(a^{3} - 0,64)\]
\[\textbf{г)}\ y^{7} - 1\frac{7}{9}y^{5} = y^{7} - \frac{16}{9}y^{5} =\]
\[= y^{5} \cdot \left( y^{2} - \frac{16}{9} \right) = y^{5} \cdot\]
\[\cdot \left( y - \frac{4}{3} \right)\left( y + \frac{4}{3} \right)\]