A linear dynamical system can be represented by the equations
Dx / dt = A(t)x(t) + B(t)u(t), y(t) = C(t)x(t) + D(t)u(t),
where A is an n × n variable matrix, B is an n × r variable matrix, C is an m × n variable matrix, D is an m × r variable matrix, x is an n-dimensional vector variable, y is an m-dimensional vector variable, and u is an r-dimensional vector variable. For the system to be stable, the matrix A must have all its eigenvalues with nonpositive real part for all t. Is the system stable if
a.

b.

-1 20] 9 A(t) = |-25-7 41? 0 0-5 -1 100 0 2 0 0-5 A(t) = | 0 1