HP 39g Master Manual page 326

We can now use the LINSOLVE function to
find A and B. While the second linear equation
is still highlighted, fetch the LINSOLVE
command from the menu. Then press
left arrow once and up arrow twice to highlight
the linear expression again as shown right.
Now, while the entire expression is highlighted,
as shown above, press SHIFT (-) to obtain
the 'AND'. The result should be as shown right.
If yours looks like the version shown to the
right then the error has been caused by not
having the whole expression highlighted before
pressing AND. Press DEL to remove the AND,
then do it properly.
The other equation is still available from the CAS History. To fetch it, press
HOME and highlight the equation. Pressing will echo it to the point of
the cursor. Note that if any portion of the expression in the editor is
highlighted when you perform an then it will be replaced by the new
expression being echoed.
We can then finish off the LINSOLVE command by pressing right arrow to
move to the second parameter position and then entering "A B". At
AND
that point we can press ENTER to obtain the values of A and B.
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