HP 15c - Manual (Page 183)

Section 13: Finding the Roots of an Equation 183
Keystrokes Display
´_ 0 5.0000
The desired root.
After the routine finds and displays the root, you can ensure that the
displayed number is indeed a root of f(x) = 0 by checking the stack. You have
seen that the display (X-register) contains the desired root. The Y-register
contains a previous estimate of the root, which should be very close to the
displayed root. The Z-register contains the value of your function
evaluated at the displayed root.
Keystrokes Display
) 5.0000 A previous estimate of the
root.
) 0.0000 Value of the function at the
root showing that f(x) = 0.
Quadratic equations, such as the one you are solving, can have two roots. If
you specify two new initial estimates, you can check for a second root. Try
estimates of 0 and -10 to look for a negative root.
Keystrokes Display
0
v 0.0000
Initial estimates.
10
“ –10
´ _ 0 –2.0000
The second root.
) –2.0000
A previous estimate of the
root.
) 0.0000
Value of f(x) at second root.