See that all る changed to り here. If these verbs were so called 'ru-verbs', the る would have been dropped altogether and they would have been inflected like this:
帰ます; 切ます; しゃべます; 入ます
...which is incorrect, and thus they must be so called 'u-verbs'. Hope that answers you question.
Hi. Let's inflect them and
Hi. Let's inflect them and see:
帰る -> 帰ります
切る -> 切ります
しゃべる -> しゃべります
入る -> 入ります
See that all る changed to り here. If these verbs were so called 'ru-verbs', the る would have been dropped altogether and they would have been inflected like this:
帰ます; 切ます; しゃべます; 入ます
...which is incorrect, and thus they must be so called 'u-verbs'. Hope that answers you question.