Learn Turkish: Makbuzu onaylanan müşteri, faturayı masaya bırakarak çıktı. - The customer whose receipt was approved left, leaving the invoice on the table.

This is the Turkish way to say "whose": you pair a possessed noun with an -(y)An participle. Makbuz gets the 3rd-person possessive suffix -u ("his/her receipt"). Then we use onaylanan ("that was approved"). Literally, it is "the his-receipt-that-was-approved customer," which in English becomes "the customer whose receipt was approved."

Why do we use the passive verb onaylanan here instead of the active onaylayan?

The word makbuz (receipt) is the subject of the relative clause, but a receipt cannot approve anything itself; it is approved by someone else. So we take the passive verb onaylanmak (to be approved) and add the relative suffix -an to get onaylanan.

What is the function of the -arak suffix in bırakarak?

The suffix -(y)Arak attaches to verbs to show how the main action was performed, similar to "while doing" or "by doing" in English. It links the customer's two actions: they left the building (çıktı) while leaving the invoice on the table (bırakarak).

Why does faturayı have the -yı ending while makbuzu has the -u ending?