〜ていく te iku
〜ていく（te iku）means “to go on ~ing; to ~ away (movement/change away from now or speaker)”. て-form + いく. Formation: V（て形）+ いく
to go on ~ing; to ~ away (movement/change away from now or speaker)
N4Formation
V（て形）+ いく
Explanation
て-form + いく. Three uses: (1) do something and then go (買って行く = buy and go); (2) movement away from the speaker (飛んでいく = fly away); (3) a change continuing from now into the future (増えていく = keep increasing). The opposite direction is 〜てくる.
Examples
Note
For changes, ていく looks toward the future; てくる traces a change up to the present (寒くなってきた = it's gotten cold).
FAQ
〜ていく — what does it mean and how is it used?
to go on ~ing; to ~ away (movement/change away from now or speaker). て-form + いく. Three uses: (1) do something and then go (買って行く = buy and go); (2) movement away from the speaker (飛んでいく = fly away); (3) a change continuing from now into the future (増えていく = keep increasing). The opposite direction is 〜てくる.
〜ていく — how do you form it?
V（て形）+ いく
〜ていく — any usage notes?
For changes, ていく looks toward the future; てくる traces a change up to the present (寒くなってきた = it's gotten cold).