**Casio fx-991EX Classwiz: Simple Programming With Mutli-Statements**

Formula Programming

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.

**Formula 1**

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] [ ∫ ] ( : ).

Set up:

B=2A²+1:C=B÷(B-1)

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.

Keystrokes:

[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.

Examples

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))

Inputs:

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.

Set up:

B=e^(-A÷(Cx)):Y÷(1-B):Y÷B

[CALC]

Example

Inputs:

A = 5 s

C = 2.6 μF

x = 10 kΩ

y = 30 V

Results:

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 )

where

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

Therefore:

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:

A=E-F:B=E+F:1÷2*(sin(A)²÷sin(B)²+tan(A)²÷tan(B)²) [CALC]

Example:

For this example, the calculator is Degrees mode.

Inputs:

E = 35° (θi)

F = 22° (θt)

Results:

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

Eddie

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