Ответ:

  1. \(6^3+(-8)^2=216+64=280\).
  2. \((8-9)^3=(-1)^3=-1\).
  3. \((-2\frac12)^2-(1\frac14)^2=\left(-\frac52\right)^2-\left(\frac54\right)^2=\frac{25}{4}-\frac{25}{16}=\frac{75}{16}=4\frac{11}{16}\).