Polyhedron what are they

In geometry, a polyhedron is a three-dimensional shape with flat polygonal faces, straight edges and sharp corners or vertices. The word polyhedron comes from the Classical Greek πολύεδρον, as poly- + -hedron. A convex polyhedron is the convex hull of finitely many points, not all on the same plane.

A polyhedron is a 3-D shape with flat polygonal faces (think complete flat shapes with no curvatures), straight edges, and sharp vertices (corners).

step by step explanation: when u removing the parentheses and combined them that would be : x+3y-x-y=2y

given the equation is 8+9z=-6, the first step would be to subtract the 8 from both sides:

8+9z-8=-6-8

since 8 minus 8 = 0, this would cancel out the 8. and since -6 minus 8 equals -14, the equation would look like this

9z = -14