Grandpa Hua said: Mathematics is a subject that China people are good at. Ask the students to solve an ancient problem of arithmetic in nine chapters: "Today, the wood is two feet, three feet around, down to Ge Sheng, and the wood is surrounded by seven, and the top is flush with the wood. Ask Long song geometry? " Vernacular translation: As the picture shows, a cylindrical wooden stick stands upright on the ground, with a height of 20 feet and a circumference of 3 feet at the bottom of the column. Gegen was born at point A at the bottom of the cylinder and wound around the cylinder at the same distance, just reaching point B at the top and bottom of the cylinder. What is the length of pueraria lobata?

As shown in the picture, a right-angled side (that is, the height of the stick) is 20 feet long.

The length of the other right angle side is 7×3=2 1 (feet),

So kudzu vine is long? √(20? +2 1? ) =29 (feet).