Ответ:

1) \(\left(\frac76\right)^9\left(\frac67\right)^{10}=\frac67\).

2) \(5^{14}\cdot\left(\frac15\right)^{12}=5^2=25\).

3) \(\left(-\frac43\right)^5\left(\frac34\right)^8=-\left(\frac34\right)^3=-\frac{27}{64}\).