The set of all real numbers greater than or equal to $-2.8$ in set-builder notation is:

$\{ x \in \mathbb{R} \mid x \geq -2.8 \}$

This reads as "the set of all $x$ in the set of real numbers such that $x$ is greater than or equal to $-2.8$."

Would you like more details or have any questions? Here are some related questions you might find interesting:

1. How would you write the set of all real numbers less than 5 in set-builder notation?
2. Can you express the set of all integers between $-3$ and $7$ (inclusive) using set-builder notation?
3. What is the difference between interval notation and set-builder notation for describing sets?
4. How would you write the set of all positive even integers in set-builder notation?
5. How can you express the set of all real numbers except $-2.8$ in set-builder notation?

Tip: Set-builder notation is a powerful tool for describing sets with specific properties or constraints, especially when working with infinite sets.