Slate (writing) Slate (writing) A slate is a thin piece of hard flat material, such as the rock also called slate, that is used as a medium for writing. The rock is “a metamorphic rock created by the recrystallization of the minerals in shale from clay to parallel-aligned, flat, flake-like minerals such as mica”. The writing slate consisted of a piece of slate, typically either 4x6 inches or 7x10 inches, encased in a wooden frame. A precise date range for writing slates of this type has not been established. Usually, a piece of cloth or slate sponge was used to clean it
Polarization of an algebraic form "n" variables u = ("u", "u", ..., "u"). Suppose that "f" is homogeneous of degree "d", which means that Let u, u, ..., u be a collection of indeterminates with u = ("u", "u", ..., "u"), so that there are "dn" variables altogether. The polar form of "f" is a polynomial which is linear separately in each u (i.e., "F" is multilinear), symmetric in the u, and such that The polar form of "f" is given by the following construction In other words, "F" is a constant multiple of the coefficient of λ λ...λ in the expansion of "f"(λu +