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.
2
As an example, we will enter the equation
A
*
B
C
+ = ⋅
5*
B
into
E1
. Suppose 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 in the
NUM
view 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
(circled) that the active variable is
B
. In this case substitution means that
2
+ = ⋅
5*
B
becomes
0 4
B
2
−
1
=
0 5*
B
. The left side is
A
*
B
C
⋅
⋅
quadratic, while the right is linear.
In this case there are clearly two points where the graphs intersect and
hence where the left and right sides are equal.
Move the cursor near to the left hand intersection and then change back
to the
NUM
view. When you do so, the approximate value you chose
with the cursor is transferred as your first ‘guess’.
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