The system of two equations
is an example of a linear system of ordinary differential equations
(because it involved derivatives).
A solution of (1) is a pair of two differentiable functions
and
which satisfy the two equations.
You can think about the system geometrically:
Suppose that the ,
plane is the surface of the sea, and the
velocity vector of the water at any point
is
A solution
is a parametrized curve in
indicating the path of a raft
floating on the surface of the sea. The system (1) reads:
If the solution passes through the point with coordinates
at time t, then its velocity vector at that time is equal to the velocity
vector of the water at that point.
The system of equations can be written in matrix form: (where x' stands for
)
A pair of functions and
is a solution of (1)
if and only if the vector valued function
is a solution of (2).
Hint: Simply plug
for
on both sides of the equation. Recall the Chain Rule:
It is easy to check that the sum of two (vector valued) solutions of (2) is again a solution of (2). Conclude that
is a solution for any choice of
constants and
.