With the use of the [CALC] key and multi-statment feature on the Casio fx-991EX, we can make simple temporary formula programs for repeated calculations. Emphasis is on the word temporary: once we go on to another mode, or press [ ON ], the formula disappears.
There are also no comparison operators or loops to work with.
Given these limitations, we can still program simple formulas with the fx-991EX.
You are going to want to be in Norm mode for this.
Note: This feature is present on other advanced solar calculators, however we will focus on the fx-991 EX Classwiz.
Let’s illustrate formula programming with some examples.
Let’s start with a simple example.
B(A) = 2A² + 1
C(B) = B/(B – 1)
To assign variables in multi-step calculations, use the syntax:
var = value.
The equals symbol can be found by pressing pressing [ALPHA] [CALC] ( = ). This is NOT the same as the equals key on the bottom right hand corner of the keyboard.
Each calculation is separated by a colon (:). Type a colon by pressing [ALPHA] [ ∫ ] ( : ).
Each variable that is not assigned will be prompted for in the order that they are typed. In the expression above, B and C are assigned while A is not. Pressing [CALC] will prompt the user to enter a value for A.
[ALPHA] ( B ) [ALPHA] ( = ) 2 [ALPHA] ( A ) [ x² ] [ + ] 1 [ALPHA] ( : ) [ALPHA] ( C ) [ALPHA] ( = ) [ALPHA] ( B ) [ ÷ [ [ ( ] [ [ALPHA] ( B ) [ – ] 1 [ ) ] [ CALC ]
Note: For this to work, press [ CALC ], not the EXE key.
You will be prompted for A. The results for B and C will be displayed.
Example 1: A = 3
[CALC], enter 3, press [ = ]
B: 19, press [ = ]
C: 19/18 [ S ←→ D ] 1.0555555556
Example 2: A = -6
Results: B = 73, C = 73/12 ≈ 1.013888889
R-C Circuit: Voltage Charge and Discharge
The charge and discharge of an R-C time circuit are described by the following equations:
Charge = Y / ( 1 – B)
Discharge = Y / B
where B = e^(-A / (C*X))
A = time (s)
X = resistance (kΩ)
C = capacitance (μF)
Y = voltage across the capacitor (V)
In this example, B is going to be used as the temporary variable.
A = 5 s
C = 2.6 μF
x = 10 kΩ
y = 30 V
B = 0.825052967 (sub-formula, press [ = ] )
171.4804732 V (voltage charge, press [ = ] )
36.36130188 V (voltage discharge)
Solar Energy: % of Solar Light Reflected
The proportion of solar light reflected off the surface is calculated by:
T = 1/2 ( sin(E – F)^2 / sin(E + F)^2 + tan(E – F)^2 / tan(E + F)^2 )
E = the angle of incidence (θi)
F = the angle of refraction (θt)
We can use Snell’s law in connection with the equation above.
Since both E-F and E+F repeat, we can assign temporary variables, such as:
A = E – F
B = E + F
T = 1/2 ( sin(A)^2 / sin(B)^2 + tan(A)^2 / tan(B)^2 )
And the set up for the fx-991EX Classwiz is:
For this example, the calculator is Degrees mode.
E = 35° (θi)
F = 22° (θt)
A = E-F = 13
B = E+F = 57
0.04721102683 (% of reflected light)
Source (for R-C Circuit and Solar Energy)
Rosenstein, Morton Computing with the Scientific Calculator Casio. 1986. ISBN: 978-1124164130
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