Texas Instruments TI-89 Titanium User Manual page 416

2. On the applicable lines in the Y= Editor,
define the system of equations as:
y1' = y2
y2' = y3
y3' = y4
– up to –
yn ' = your nth-order equation
Based on the above substitutions, the y' lines in the Y= Editor represent:
Note:
y1' = y'
y2' = y''
etc.
Therefore, this example's 2nd-order equation is entered on the y2' line.
In a system such as this, the solution to the y1' equation is the solution to the nth-order
equation. You may want to deselect any other equations in the system.
Example of a 2nd-Order Equation
The 2nd-order differential equation y''+y = 0 represents a simple harmonic oscillator.
Transform this into a system of equations for the Y= Editor. Then, graph the solution for
initial conditions y(0) = 0 and y'(0) = 1.
Differential Equation Graphing 413