HP 33s - Manual (Page 326)

D–2 More about Solving
f (x)
x
a
f (x)
b
x
f (x)
x
c
f (x)
x
d
Function Whose Roots Can Be Found
In most situations, the calculated root is an accurate estimate of the theoretical,
infinitely precise root of the equation. An "ideal" solution is one for which f(x) = 0.
However, a very small non–zero value for f(x) is often acceptable because it might
result from approximating numbers with limited (12–digit) precision.