1:
a: \(\left(-\dfrac{3}{4}\right)^4:\left(-\dfrac{9}{8}\right)^4=\left(\dfrac{-3}{4}\cdot\dfrac{-8}{9}\right)^4=\left(\dfrac{2}{3}\right)^4\)
b: \(\left(\dfrac{7}{8}\right)^5:\left(\dfrac{21}{16}\right)^5=\left(\dfrac{7}{8}\cdot\dfrac{16}{21}\right)^5=\left(\dfrac{2}{3}\right)^5\)