Final answer:
Macbeth uses a hyperbole to express his fear and concern over the possibility that Banquo's descendants will have power in the future.
Step-by-step explanation:
In the final line, Macbeth uses a hyperbole to express his fear and concern over the possibility that Banquo's descendants will have power in the future. The phrase 'crack of doom' is a metaphor for the end of time, suggesting that Macbeth believes this line of descendants will continue until the end of the world. Despite what it seems, Macbeth is disturbed by the idea that Banquo's descendants will hold power, as it threatens his own reign and belief in his succession.
Learn more about Macbeth's reaction to the vision shown by the Weird Sisters