Learn Farsi: با چنین عقلی، چطور این توهم را باور کردی؟ - With such an intellect, how did you believe this hallucination?

چنین (chenin - such/this kind of) behaves like a demonstrative adjective, much like این (this) and آن (that). It is placed directly before the noun it modifies and never connects to it with an Ezafe.

Why is there an -i suffix at the end of aghl to make it aghli?

That is the indefinite -ی (-i) suffix meaning 'a' or 'an'. In Farsi, when you use چنین (chenin) or چنان (chenân) to mean 'such a [noun]', it is standard practice to attach this indefinite -i to the end of the noun, creating چنین عقلی (such an intellect).

Does tavahhom refer to a medical hallucination here?

It can medically mean hallucination, but in everyday conversational Farsi, توهم (tavahhom) is heavily used metaphorically. It typically means a 'delusion', 'illusion', or a completely absurd false belief. The speaker is likely teasing or criticizing the listener's poor judgment.

Why is the object marker ra placed right in the middle of the phrase?

The verb is the compound باور کردن (bâvar kardan - to believe). The direct object is این توهم (this hallucination). Because the object is highly specific (indicated by the demonstrative این), it requires the definite object marker را (râ) immediately after it, before the verb.