√81p¹²q²⁶ -------- 49

$$\sqrt{\frac{81p^{12}q^{26}}{49}} = \frac{\sqrt{81p^{12}q^{26}}}{\sqrt{49}} = \frac{\sqrt{81} \cdot \sqrt{p^{12}} \cdot \sqrt{q^{26}}}{7} = \frac{9p^6q^{13}}{7}$$

Ответ: $$\frac{9p^6q^{13}}{7}$$