I found this sentence in Tofugu's workbook.
My question is: Why is the る not dropped so it becomes 見に, as in this sentence:
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"～しに行く" = the 連用形(continuative form) of a verb + に行く and it means "go ～ing", so 見に行く = 見 (the 連用形 of 見る) + に行く.
The "には" of "the 連体形(attributive form) of a verb + には" is used for the object of the action. For example, 車が走るには、ガソリンが必要です.
Because it's 見るには and not verb + に + いく。They're completely different things. Verb + には is it's own thing. It means like 'in order to x / to accomplish x'. This is something that is extremely unintuitive at first but it makes a bit more sense when you think about how には is used with regards to physical objects. には is used to indicate that something is inside something else or that something is placed in a physical location. So for example 「この箱にはおもちゃがある」"There are toys in this box". So, how does it apply to verbs? Well.. this explanation might not make a lot of sense but if you kind of think of it like 'in order to embody this action (that is, to be inside the action, living it,physically performing it) you need to do X. Is kind of the gist of it.