Which of the following statements describes a compound machine?
a. it has movement in only one direction.
b. it can only be acted on by one force.
c. it is made up of more than one simple machine.
d. it makes work more difficult.

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.