What is the definition for volume and density

volume :: is the level at which something is heard or the amount of space that something takes up.

Density :: is a measure of mass per volume. The average density of an object equals its total mass divided by its total volume.

The density, of a substance is its mass per unit volume. The symbol most often used for density is ρ, although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume: {\displaystyle \rho ={\frac {m}{V}}} where ρ is the density, m is the mass, and V is the volume

i think it because equal matrices have equal dimensions, only square matrices can be symmetric. for all indices and . every square diagonal matrix is symmetric, since all off-diagonal elements are zero. in linear algebra, a real symmetric matrix represents a self-adjoint operator over a real inner product space.

are their multiple choices ?

explanation: