3) -7x263³; 2yzs

3) $$\left(-\frac{7x^2b^3}{2y^4z^5}\right)^3 = - \frac{(7x^2b^3)^3}{(2y^4z^5)^3} = -\frac{7^3(x^2)^3(b^3)^3}{2^3(y^4)^3(z^5)^3} = - \frac{343x^6b^9}{8y^{12}z^{15}}$$

Ответ: $$- \frac{343x^6b^9}{8y^{12}z^{15}}$$