Final answer:
Macbeth is angered and frustrated when he discovers that Macduff has fled, viewing him as a threat and deciding to act with violence.
Step-by-step explanation:
When Macbeth learns that Macduff has fled to England, Macbeth reacts with frustration and anger, realizing the threat Macduff poses to his reign. Macbeth's growing paranoia and fear of losing his power are evident as he decides to act swiftly and violently, demonstrating the tragic hero's further descent into tyranny and madness. This moment in the play underscores Macbeth's determination to crush any opposition, a decision that only propels him further along a path of destruction and despair.