HP 15c - Manual (Page 16)

16 Section 1: Using _ Effectively
16
Keystrokes Display
− 278.4497 Last estimate tried.
) 276.7942 A previous estimate.
) 7.8948 Nonzero value of function.
|(|( 278.4497 Restores stack to original state.
´_A Error 8 Again, no root found.
− 278.4398 Approximately same estimate.
) 278.4497 A previous estimate.
) 7.8948 Same function value.
You have found a positive local minimum rather than a root. Now try to find the negative
root
Keystrokes Display
1000 ”v -1,000.0000
1100
” -1,100 Two larger, negative estimates.
´_A -108.9441 Negative root.
) -108.9441 Same previous estimate.
) 1.6000 -08 Function value.
There is no need to search further—you have found all possible roots. The negative root has
no meaning since it is outside of the range for which the declination approximation is valid.
The graph of the function confirms the results you have found.
Solving a System of Equations
_ is designed to find a single variable value that satisfies a single equation. If a
problem involves a system of equations with several variables, you may still be able to
_ to find a solution.