The heart-shaped line is the trajectory formed by a fixed point on a circle when it rolls around another circle that is tangent to it and has the same radius. It is named after its shape like a heart. Derived from the thirteenth letter written by Descartes to Princess Christine of Sweden, r=a(1-cosθ). The functional expression he wrote on the title page of his mathematics book is the most obscure and useless confession. This is the story of a top student who was forcibly bent by another top student. He was sultry and awkward and was attacked by a gangster and a mean spirit.