What was Yehoshua's answer?
Rashi: Go clear out the forest and build cities there.
Rashi (18, citing Sotah 36b): If you are populous, hide yourselves in forests, lest Ayin ha'Ra harm you.
Radak: Refer to 17:14:3:1.
Bi'ur ha'Gra: According to your words [that you are populous], you should not receive more (for you can take from the Perizi and Refa'im).
Malbim: Go clear out the forest and plant fields there.
What is the meaning of "u'Vereisa"?
Rashi: You will cut off, like in Yechezkel 23:47.
Radak citing Targum Yonasan: Prepare [for yourselves].
Radak: It is choice, like "Baru Lachem Ish" (Shmuel 1 17:8).
Malbim: You will create 1 [a new land of fields and vineyards, through cutting and uprooting the trees.
Only Hashem can be Borei (create from nothing)! People merely form [from what already exists]! Perhaps here it is used metaphorically, for now the forest is not at all proper to farm, so it is as if you will create farm land. (PF)
What is the meaning of "Atz"?
Rashi: [If in your current borders you are] cramped.
Metzudas Tziyon: It hints to rapidity