need的否定形式可以是need need to do sth为啥在否定形式时不可以呢?need doing sth在否定形式时

题目

need的否定形式可以是need need to do sth为啥在否定形式时不可以呢?need doing sth在否定形式时
怎样才能判断need to do sth与need doing sth?
例题：1.He does not need________(do) too much homework.
2.You need to eat more vegetbables.(改为否定句

答案

1.to do.
2.You need not to eat more vegetables.
(你蔬菜英语打错了)