HP -225 Owner's Manual page 172

f(x) f(x)
4a 4b
f(x)
4c
Figure B-4. Conditions Where Can't Find a Root
In addition to the NO ROOT FHND error, may return a math
error if an estimate produces an unallowed operation—for example,
division by 0, square root of a negative number, or logarithm of 0.
You should keep in mind that can generate estimates over a
wide range. You can sometimes avoid math errors by using very good
guesses. If returns a math error, press unknown variable to
see the value that produced the error.
Example: A Relative Minimum. Calculate the root of the equation:
x2 —6x + 13 =0
164 B: More About Solving Equations