Is the dividing line of the puzzle in the first grade mathematics a dotted line or a solid line?

When drawing a math problem, use a solid line for what you can see directly and a dotted line for what you can't see directly. A solid line is real, for example, the edge of an object is a solid line, and the sunlight is a dotted line.

Tangram is an ancient traditional intellectual toy in China. As the name implies, it consists of seven boards. These seven boards can be combined into many figures, such as triangles, parallelograms and irregular polygons. Players can also combine them into various figures, images, animals, bridges, houses, towers and so on. And some Chinese and English letters. Tangram was invented by the working people in ancient China, and its history can be traced back to at least the first century BC, and it was basically finalized in the Ming Dynasty.