2) $$(\frac{1}{7}x^5 - z^2)(\frac{1}{7}x^5 + z^2) = (\frac{1}{7}x^5)^2 - (z^2)^2 = \frac{1}{49}x^{10} - z^4$$
Ответ: $$\frac{1}{49}x^{10} - z^4$$