This paper presents various results on foot polygons, ie polygons whose vertex tips are perpendiculars lowered from a point in the plane to the sides of a polygon. In most cases, these are quadrilaterals, but there are results that apply to n-terracots in general. Many theorems on knife triangles have long been known in the Euclidean geometry of triangles, so a part of such results is presented in the first chapter. Let us emphasize the inequality known as the Erdoes-Mordell theorem, since later in the paper we prove a theorem for tendon quadrilaterals that can be considered as a kind of analogue of this inequality. Let us point out another proof of the property of a quadrilateral, different from a parallelogram, that there is exactly one point with the property that the blades of the perpendiculars on the sides of the quadrilateral are collinear points. By analogy with a known property from the geometry of a triangle, this unique point is called the Simson point, and the direction on which the perpendicular blades lie is called the Simson direction of the quadrilateral. Different inequalities for n-terracots that are analogous to the known results for quadrilaterals and Steiner's theorem on a circle formed by points whose associated knife polygons have a constant surface have been proved.