Final answer:
The instrument that is symbolic of Russian folk music and has a triangular body is the Balalaika. It is characterized by its shape and three strings, and plays a significant role in Russian cultural traditions.
Step-by-step explanation:
The triangular-bodied lute symbolic of Russian folk music is the Balalaika. This instrument has been a prominent feature in Russian culture and is often associated with traditional Russian folk songs. The Balalaika can be identified by its distinct triangular body and three strings, and it is played by plucking or strumming. Comparable historical stringed instruments like the Byzantine lyra have evolved through the centuries, giving rise to a diverse family of lutes and lyres that hold cultural significance in various regions, just like the Balalaika does in Russia.