HP 33s - Manual (Page 120)

7–10 Solving Equations
Keys: Display: Description:
)
 This value from the Y–register is
the estimate made just prior to
the final result. Since it is the
same as the solution, the
solution is an exact root.
)
 This value from the Z–register
shows the equation equals zero
at the root.
The dimensions of the desired box are 50 Ч 10 Ч 15 cm. If you ignored the upper
limit on the height (20 cm) and used initial estimates of 30 and 40 cm, you would
obtain a height of 42.0256 cm — a root that is physically meaningless. If you
used small initial estimates such as 0 and 10 cm, you would obtain a height of
2.9774 cm — producing an undesirably short, flat box.
If you don't know what guesses to use, you can use a graph to help understand the
behavior of the equation. Evaluate your equation for several values of the
unknown. For each point on the graph, display the equation and press
X —
at the prompt for x enter the x–coordinate, and then obtain the corresponding
value of the equation, the y–coordinate. For the problem above, you would always
set V = 7500 and vary the value of H to produce different values for the equation.
Remember that the value for this equation is the difference between the left and
right sides of the equation. The plot of the value of this equation looks like this.
7500 _ (40_ ) (20_ ) 4 H H H
20,000
_10,000
50
H
_10