Does جدًا follow in case??

In homework 4 regarding the sentence 'The big knife is very sharp' جدًا الكبيرحادُّّ السكِّين why is 'very sharp' جدًا حادُّّ not agreeing with each other in terms of case?

جدًاnever changes, just another one of those word you do get in arabic

السلام عليكم

جداً does not 'agree in case' with a noun because it is not an adjective.
It is an special type of adverb which intensifies the adjective it appears after. It will always be fixed on fathah. Another example is: كثيراً (a lot).

والسلام

Please do not say that they are fixed upon fathah. This is actually not the case.

Words that are fixed upon fathah are those such as, هوَ أنتَ كتبَ, etc

The words you have given are actually accusative and therefore in a state of accusativity. The rule of why this is yet to be taught. But you are on the correct lines of thought by mentioning adverbs.



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