Hydrogen fuel cells are used on the space shuttle to provide the shuttle with all of its electrical energy. Explain why fuel cells are used instead of batteries.

Hydrogen used in fuel cells has the energy to weight ratio ten times greater than lithium-ion batteries. Consequently, it offers much greater range while being lighter and occupying smaller volumes. It can also be recharged in a few minutes, similarly to gasoline vehicles.

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.