# How To Use Scientific Calculator (Casio fx-991 MS)

## Introduction

The Scientific Calculator is an advanced version of an ordinary calculator which helps us to solve complex arithmetic problems.

The Normal Calculator consists of only four basic operations i.e Addition, Subtraction, Multiplication, and Division.

In the case of Scientific Calculator, we can solve complex equation (a+i b), Matrices, Logarithmic Problems, Trigonometric Problems and Problems involving iterations.

Note: Scientific Calculators also have a certain limit. For higher-order problems, scientific calculators cannot be used.

In order to solve, higher-order problems theorems should be followed.

In this module, I am going to work with the Scientific Calculator from Casio fx-991 MS for the demonstration purpose.

If you are using any other version from Casio don’t worry the basic functions and operations would be the same but the there be will a small deviation in keys and usage.

I have been using this Casio fx-991 MS whole of my Bachelor’s degree in Electrical and Electronics Engineering and I recommend you guys to go with this version.

## How to check original Casio fx-991MS

While purchasing Casio fx-991 MS, check whether the product is original or duplicate by using these simple trick for checking original calculator or not.

• Press SHIFT, ON, and 7 at the same time.
• You will get a screen which shows, DIAGNOSTIC AC.
• Now press the button 9.
• Then press the SHIFT till you get the AC. (Press 3 times to get the AC)
• Then again press AC twice.
• Now you will get a screen which shows 00.
• Now Press SHIFT. (You can see 01 on the screen)
• Now Press ALPHA. (You can see 02 on the Screen)
• Then UP Arrow, RIGHT Arrow, MODE. (You can see 03, 04, 05 respectively)
• Now Don’t press ON button. If you have pressed mistakenly, again start from the first.
• Then CALC, d/dx, LEFT Arrow, RIGHT Arrow. (You can see 06, 07, 08, 09)
• Then x inverse, CONST, and press till you TEST OK.
• If you get this TEST OK message then your Calculator is Original.

## Basics of Scientific Calculator

### How to switch ON your calculator

To Switch ON your fx-991 MS Scientific calculator, just press the ON button.

### How to Switch OFF your calculator

To Switch OFF your fx-991 MS Scientific calculator, press the SHIFT button and AC button at a time.

Your Calculator will automatically get Switch OFF after a few hours of idle. It’s better to switch OFF when devices are not in use.

## Four Basic Operations in Fx-991 MS Scientific Calculator

To perform Addition, use the Addition operator (+). Press the Operand 1, Addition Operator (+) and the Operand 2. Finally, press equal to (=) to get the answer.

For “n” number of operands,

Operand 1 +  Operand 2 + Operand 3 ……….+ Operand n = Answer.

### Subtraction

To perform Subtraction, use the Subtraction operator (-). Press the Operand 1, Subtraction Operator (-) and the Operand 2. Finally, press this equal to (=) symbol to get the answer.

For “n” number of operands,

Operand 1 – Operand2 – Operand 3 …………- Operand n = Answer.

### Multiplication

To perform Multiplication, use the Multiplication operator (*). Press the Operand 1, Multiplication Operator (*) and the Operand 2. Finally, press this equal to (=) symbol to get the answer.

For “n” number of operands,

Operand 1 * Operand 2 *  Operand 3 …………* Operand n = Answer.

### Division

To perform Division, use the Division operator (/). Press the Operand 1, Division Operator (/) and the Operand 2. Finally, press this equal to (=) symbol to get the answer.

For “n” number of operands,

Operand 1 / Operand 2 / Operand 3………………../Operand n = Answer.

(or )

Operand 1 / Operand 2 = Ans then Ans/Operand 3 = Answer and the cycle goes on.

## Working With Mode in Casio fx-991 MS

### Mode Initialization

Press Mode and then choose the required operation by pressing the corresponding number.

Use the mode button to go next screen.

• In the first screen, you can see COMP and CMPLX.
• Now press the Mode button again.
• In the second screen, you can see SD, REG, and BASE.
• Press the Mode button.
• In the third screen, you can see EQN, MAT, and VCT.
• Mode button Again.
• In the fourth screen, you can see Deg, Rad, and Gra.
• Mode button Again.
• In the fifth screen, you can see Fix, Sci, and Norm.
• Mode button now.
• In the Sixth screen, you can see Disp and CONT.

### Mode Clear in Casio fx-991 MS

Use the following command to clear the mode.

• Press SHIFT and MODE at the same time.
• You can see Mcl, Mode, and All.
• Now press 2 to clear the Mode.

## Working With Memory in Casio fx-991 MS

### To Clear the memory in Casio fx-991 MS

• Press the SHIFT button and the MODE button at the same time.
• You can see Mcl, Mode, and All.
• Now press the button 1 to clear the Memory.

### How to Reset the Casio fx-991 MS

• Press the SHIFT button and the MODE button at the same time.
• You can see Mcl, Mode, and All.
• Now press the button 3 to Reset your Calculator.
• Then press equal to a button.
• You can see the RESET ALL in the display screen.
• Now you have successfully made RESET.

## Working with EQN in fx-991 MS

We can solve an equation with up to 3 unknowns and 3 degrees using this scientific calculator.

### Solving Linear Equation using fx-991 MS

Let us see how to solve an equation with 2 unknowns.

Go to EQN and choose. (If you have any doubt just refer Mode Initialization section)

For example, I am going to solve this equation.

2x + 4y – 1 = 0

3x + 5y + 3 = 0

Choose 2 unknowns in the EQN category i.e, x and y.

a1x + b1y + c1 = 0

a2x + b2y + c2 = 0

For a1 enter 2

For b1 enter 2

For c1 enter -1

For a2 enter 3

For b2 enter 5

For c2 enter 3

Ans: x=8.5, y= -4.5

Follow the same steps for 3 unknowns.

### Solving non-linear equations using fx-991 MS

Let us see how to solve the non-linear equation of order 2.

For example, I am going to solve the following equation.

2x² + 3x + 4 = 0

ax² + bx + c = 0

For a enter 2

For b enter 3

For c enter 4

Ans: x1 = – 0.75 , x2 = – 0.75

Follow the same steps for the order of degree 3.

Try different problems by using the same method.

## Working with Matrix in fx-991 MS

Refer the Mode Initialization section and go to Matrix Mode.

After going Matrix mode, press the SHIFT button and then button 4 to get a screen where you can Set Dimension, Edit, and get Matrix.

You will get the three option Dim, Edit, Mat.

### Creating a Matrix A and Matrix B in fx-991 MS

• Now Press 1 and set the Dimension.
• Then Create a Matrix A and Matrix B to perform an Operation.

For example, I am going to show how to work with

• Choose A for Matrix A and B for Matrix B by pressing the buttons 1 and 2 respectively.
• Type the m and n values, where m denotes the row and n denotes the column.
• Here I am going to types m and n values as 3.
• Then fill the values of Matrix A.
• Here I am going to fill all the values as 1. A11 =1, A12=1, A13=1, A21=1, A22=1, A23=1, A31=1, A32=1, A33=1.
• Similarly, fill the values for Matrix B.
• Here I am going to fill with 1 for all the elements in the Matrix B.
• Now you have successfully created two matrices A and B.

### Matrix Addition in fx-991 MS

Now we are going to see how to add the two matrices A and B.

• Firstly, we have to get the value of matrix A that we have created.
• To do that, Go to MAT mode and press button 4 followed by the SHIFT button.
• Then choose the MAT from the 3 options. (Press the button 3 for that)
• Select MAT A, addition operator and then MAT B.
• Now you have got the answer.
• Use the right arrow to move between different elements.
• Here I am getting all the values as 2.
• Hope you’ve also got the same.

### Matrix Subtraction in fx-991 MS

The procedure for Matrix subtraction is almost the same as the matrix addition. Only we have the replace the addition operator with the Subtraction operator.

• Get Matrix A.
• Use the Subtraction operator (-)
• Get Matrix B.
• Here I have got the answer as o in all the elements.

### Matrix Multiplication in fx-991 MS

Just replace the addition or Subtraction operator with * and follow the same steps.

MAT A * MAT B

Here I am getting 3 as an answer for all the elements.

### Matrix Inversion in fx-991 MS

There is no division in Matrix and it was replaced by Matrix Inversion.

### Steps to find Matrix Inversion

[A][B] = [C]

[B] = [C]/[A]

[B] = [C][A]-¹

• To find the A inverse, find the determinant of A.
• The determinant of A should not be zero. Then only we can find determinant.
• The find the cofactor of Matrix A.
• Then take the A Transform.

### To find Determinant using fx-991 MS

This can be done easily using the manual method.

Let me show you how to find determinant using the scientific calculator.

• Press the SHIFT button and then press 4.
• Use the right arrow button to get the determinant option.
• Choose Det by pressing button 1.
• Now you have got the Det function.
• Next, we have to get MAT A.
• You should get the following on the screen. Det  MAT A.
• I am getting 0 as an answer.

### To find Transform of Matrix using fx-991 MS

• Choose the Trn option in MAT menu.
• Now get the MAT value.
• Trn MAT A.

Note: If all the elements are the same in MAT A then the transform of MAT A equals MAT A.

[A] = [A]T

## Working with Complex Numbers (a+ i b) in fx-991 MS

Complex numbers are represented in this format (a+ i b) but in the fx-991 MS Scientific Calculator you have to follow this format (a + bi)

Use the Eng button to press the i.

Note: The button i would be displayed only if you are in the complex mode.

• Just Ensure that you are in complex mode.
• For the best practice always use brackets to enter the complex numbers.
• While getting the answer, Press SHIFT button and equal to button to check the Imaginary Value.

Now I am going to add the following two complex numbers.

(4+i3) + (3+i2)

Just enter the same in the calculator but for the complex format put the i after the number only in the calculator.

I am getting the answer as (7+i5)

### Subtracting two Complex Numbers

The Procedure for subtraction is the same as that of Addition with a slight modification.

Replace + by –

I am going to subtract these two numbers.

(4+i3) – (3 + i2)

I am getting the answer as (1+ i1)

### Multiplying two Complex Numbers

Like previously seen, the procedure for multiplying two complex is also similar to Addition and Subtraction.

Just we have to replace with multiplication operator.

I am going to multiply these two numbers.

(4+i3) * (3+i2)

I am getting the answer as (6 + i17)

### Dividing two Complex Numbers

Manual dividing the complex numbers is a little bit difficult process. We have to perform multiplication, addition, and subtraction all in that.

But in the scientific calculator, it’s a simple process.

I am going to divide the following two complex numbers.

(4+i3) / (3+i2)

I am getting the answer as 1.384 +i 0.07692

I will cover the remaining topics soon.

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