An obtuse triangle is a triangle that has one obtuse angle, meaning this angle is greater than 90 degrees but less than 180 degrees.

René Descartes was a famous French philosopher, mathematician, and physicist. He is one of the founders of modern Western philosophy. He made important contributions to the development of modern mathematics and is considered the father of analytic geometry for formalizing the coordinate system in geometry.

A polygon is a closed shape made up of three or more line segments connected end to end. Depending on different criteria, it can be divided into regular and irregular polygons, as well as convex and concave polygons.

Cartesian coordinates are a math tool used to determine the position of points with numbers, usually referring to the rectangular coordinate system. It was created by the French mathematician Descartes, and the main idea is to link geometric shapes with algebraic equations, making calculations easier.

The angles in a polygon mainly include two key concepts: interior angles and exterior angles.

David Hilbert (January 23, 1862 – February 14, 1943), born in Königsberg, East Prussia, was a mathematician

"Unit conversion ratio" is not a standard math term. It usually refers to the ratio between two values with the same dimension in a unit conversion (i.e., the conversion factor). Essentially, it's the proportional relationship of the same physical quantity in different units.

The identity element is a basic concept in algebraic structures in mathematics. It refers to a special element that doesn’t change the value of other elements under a specific operation. It’s like the “invisible person” in an operation – when combined with any element, the other element stays the same, like 0 in addition and 1 in multiplication.

Navigation is the technology or process of guiding people or devices from the starting point to the destination safely and accurately. It mainly deals with the three core questions: 'Where am I, where am I going, and how do I get there?'

Geographic coordinates are basically like giving every point on the Earth's surface a 'house number,' mainly determined by longitude and latitude. They treat the Earth as a sphere and use a grid system to tag every place with a unique numeric code. Whether it's the vast ocean or remote mountains and forests, as long as there’s a coordinate, you can pinpoint it accurately.