Formal:
* The current security system is inadequate to protect the building from intruders.
* Her explanation was inadequate, leaving many unanswered questions.
* The funding provided for the project is inadequate to meet its ambitious goals.
Informal:
* The bus service is inadequate; I have to wait for ages every morning.
* My cooking skills are inadequate, so I usually order takeout.
* He felt inadequate in his new job, lacking the experience required.
Figurative:
* The words felt inadequate to express the depth of her grief.
* Her small apartment felt inadequate for the growing family.
As you can see, "inadequate" can be used to describe something that is insufficient, deficient, or not good enough for a particular purpose. It can also be used to describe a feeling of being lacking or insufficient.