The heart can be expressed in polar coordinates: r = a (1-sin θ). The area of cardiac line with equation ρ (θ) = a (1+cos θ) is S = 3 (π a 2)/2. The center line, also called the center line, is a kind of epicycloid and a kind of hub line. It is the trajectory formed when a fixed point on a circle rolls around another circle that is tangent to it and has the same radius. It gets its name because it is shaped like a heart.

The figure of the heart-shaped line between Mandleberg sets is a heart-shaped line. The English name of cardiac thread "Cardioid" was published by deCastillon in the Journal of Theroyal Society Philosophy in 174 1 year. It means "like a heart".

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The story of heart function:

The love story of mathematician Descartes. Descartes was born in France on 1596. When the Black Death broke out in continental Europe, he wandered to Sweden and met Princess Christine, a small principality of Sweden. She was 18 years old and later became her math teacher. Getting along with each other every day makes them fall in love. The king, the princess's father, flew into a rage and ordered Descartes to be executed. Later, she was exiled to France because of her daughter's intercession, and Princess Christine was also under house arrest by her father. Descartes fell seriously ill soon after he returned to France. He writes to the princess every day. Because she was intercepted by the king, Christine never received a letter from Descartes.

Descartes died after sending the 13 letter to Christine. The letter 13 only contains a short formula: r = a (1-sin θ). The king couldn't understand that they didn't always talk about love, so he gave this letter to Christine, who had been depressed. As soon as the princess saw it, she immediately understood the intention of her lover. She immediately began to draw a diagram of the equation. She was very happy when she saw the chart. She knows that her lover still loves her. The graph of the equation is a heart. This is also the famous "heart line".