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The flow lines (or streamlines) of a vector field are the paths followed by a particle whose velocity field is the given vector field. Thus the vectors in a vector field are tangent to the flow lines. If parametric equations of a flow line are x = x(t), y = y(t) explain why these functions satisfy the differential equations dx/dt=x and dy/dt=-y. Then solve the differential equations to find an equation of the flow line that passes through the point (1, 1).
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Verified(b) Let and the parametric equations of a flow line. By definition of the flow lines, the velocity vector of the flow line at the point is is equal to the given vector field.
As the velocity vector is given by , then we have or
Therefore, the stream lines satisfy the differential equations
and
To solve (2) we write it as
Hence, integrating we obtain
or
where and are constants.
We can solve (3) in a similar way to obtain
where is a constant.
Taking the product between (4) and (5) we have
with a constant.
Therefore, the equations for the flow lines are
If the flow line passes through (1,1) we obtain from (6)
which gives . Then, the flow line through this point has equation
At any point is the component of the velocity.
At any point is the component of the velocity.
Here it is given that Velocity at the point ) is
Note that, the component of the velocity is and
the -component of the velocity is
Therefore, we can write
Let and be the parametric equations of a flow line. The definition of the flow lines gives us that the velocity vector of the flow line at is equal to the given vector field.
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