28) \(\dfrac18\cdot\left(\dfrac12\right)^4=\)

\(\dfrac18=\left(\dfrac12\right)^3\), поэтому

\(\dfrac18\cdot\left(\dfrac12\right)^4=\left(\dfrac12\right)^{3+4}=\left(\dfrac12\right)^7=\dfrac1{128}\).

Ответ: \(\dfrac1{128}\).