A Detailed Explanation Of Plot In Solve - HP 39g Master Manual

A detailed explanation of PLOT in Solve

The PLOT view in the Solve aplet is a little
more complex than most others, since the
active variable (x, t, theta etc) changes
according to the value for which you are trying
to solve.
As an example, we will enter the equation + = ⋅ into E1. Suppose
2
A B * C 5* B
that we know the values of A and C but need to find B.
Now change to the NUM view and enter the
values shown right. Ensure that the highlight is
on B as shown and then press PLOT.
The result is a quadratic intersecting a line and
the reason for this lies in how Solve interprets
your equation.
When you select B by highlighting it, the calculator substitutes the supplied
values into all other variables except B and graphs the left and right sides of
the equation as two separate graphs. This may not always be obvious
because the substitution may produce graphs which aren't visible on the
default scale.
In the graph above you can see from the label on the horizontal axis that the
active variable is B. In this case substitution means that
+ = ⋅
2
A B * C 5* B
becomes . The left side is quadratic, while the right is linear.
⋅ − = ⋅
2
0 4 B 1 0 5* B
In this case there are clearly two points where
the graphs intersect and hence where the left
and right sides are equal.
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