Breakdown of Мы читаем об интересных идеях в этих постах.
мы
we
интересный
interesting
этот
this [f: эта, n: это]
читать
to read
Questions & Answers about Мы читаем об интересных идеях в этих постах.
Why do we use об instead of just о here?
The preposition о (about) changes to об when the next word starts with a vowel. Since интересных starts with the vowel и, we use об so the words flow together more easily when speaking.
Why do the describing words end in -ых (интересных) and -их (этих)?
These words are in the prepositional plural. For most regular adjectives like интересный, the prepositional plural ending is -ых. However, этот (this) is a special pointer word that takes the soft ending -их in the plural to become этих.
How do we know whether to add -ах or -ях to the plural nouns?
It depends on the ending of the dictionary form. Пост (post) ends in a hard consonant, so it takes the hard prepositional plural ending -ах to make постах. Идея (idea) ends in the soft vowel я, so it takes the soft ending -ях to make идеях.
Why are both parts of the sentence (об интересных идеях and в этих постах) in the prepositional case?