For ballet there are many positions a dancer must know. For example:
Dancers also need to know how high to lift their legs, we refer to that as degrees. Dancers lift their leg at 45 degrees, 90 degrees, and higher. The number is determined by the distance from the supporting leg.
Something else that relates to math is a dancers balance. Dancers have to determine where their center is and how much weight they need to distribute through out the body evenly so they can balance with out falling. This idea gets very precise, with the idea of head over shoulders over hips over feet, you even have to distribute the weight through out the feet and toes even so you dont fall!
Dancers create beautiful lines and curves done through balance.
Musicality is a major mathmatical problem for dancers, dancers have to memorize movements and counts and when to perform on what count. Usually a dancer counts in eight counts but that can easily be changed. Sometimes it is 6 counts, 5 counts, etc. Sometimes it is a combination of counts in a variation of counts. Certain movements and strong accents hit on certain beats of counts.
Over all dance is a complex art that requires music mathmatics along with dance mathmatics combined into one art to create the beautuful movements and elegant lines to create the hard-work performance so that the audience can enjoy!