Adjectives and subjects agreement, in Arabic
Hi Everybody I have a big doubt about agreement among adjectives and their subjects/objects.

If the adjective refers to a person it agrees with that in gender and number
If the adjective (as for the verbs) refers to things it goes to feminine and singular

Right?

And if the adjective refers to just one thing it agrees with that in gender and number? Or it goes to feminine singular?

and with the collective nouns as شعر ?

Question

Adjectives and subjects agreement, in Arabic
Hi Everybody I have a big doubt about agreement among adjectives and their subjects/objects.

If the adjective refers to a person it agrees with that in gender and number
If the adjective (as for the verbs) refers to things it goes to feminine and singular

Right?

And if the adjective refers to just one thing it agrees with that in gender and number? Or it goes to feminine singular?

and with the collective nouns as شعر ?

Answer

Hi, You almost map them all, as for الشعر it is muscular, in fact all nouns should be classified , but the non-human things should be feminine when they are in plural!. there is also some rules for the numbers of things . they are interesting rules . 
http://allthearabicyouneverlearnedthefirsttimearound.com/p3/p3-ch3/arabic-numbers/

Answer

It agree with gender and number in describing one thing ...
 شعر takes muscular singular