Hamlet is seen as being indecisive throughout the first three acts of the play. which of these lines from acts iv and v show that hamlet is finally focusing on revenge?

When he has dark thoughts. When he uttered these words, it was already clear that he set on revenge.  Before he departed, there were already hints in his words as well as his tone when  he answers Claudius reveals what he feels about him.

roses are red,

violets are black,

for what you said,

i hope you sit on a big fat tack.