The Casio fx-991EX is a powerful scientific calculator, capable of much more than basic arithmetic. One often-needed function is finding the Least Common Multiple (LCM) of two or more numbers. This tutorial will guide you through the process, step-by-step. We'll cover finding the LCM of two numbers, and then briefly touch upon how to extend this to more than two.
Finding the LCM of Two Numbers on the fx-991EX
The fx-991EX doesn't have a dedicated LCM button. Instead, we leverage its ability to calculate the Greatest Common Divisor (GCD) and use the relationship between GCD and LCM:
LCM(a, b) = (|a * b|) / GCD(a, b)
Where:
- a and b are the two numbers.
- |a * b| represents the absolute value of the product of a and b (this is important to handle negative numbers correctly).
- GCD(a, b) is the Greatest Common Divisor of a and b.
Here's how to do it:
-
Input the Numbers: Enter the first number, then press the multiplication symbol (×). Enter the second number. This calculates the product.
-
Find the GCD: Press the
SHIFTbutton, then the÷button (which reveals theGCDfunction). The calculator should displayGCD(, prompting you to input the two numbers whose GCD you need. You'll need to enter the numbers again, separated by a comma (,). Then press=. -
Calculate the LCM: The display will now show the GCD. To obtain the LCM, press the division symbol (
÷) and enter the GCD value displayed. Press=to get the LCM.
Example: Let's find the LCM of 12 and 18.
-
12 × 18 = This gives you 216.
-
SHIFT + ÷ (GCD) 12 , 18 = This will give you 6 (the GCD).
-
216 ÷ 6 = This will yield 36, which is the LCM of 12 and 18.
Finding the LCM of More Than Two Numbers
The fx-991EX doesn't directly support calculating the LCM of more than two numbers using a single function. However, you can achieve this by iteratively applying the two-number LCM method.
For example, to find the LCM of 12, 18, and 24:
- Find the LCM of 12 and 18 (as shown above - result: 36).
- Find the LCM of 36 and 24 using the same two-number method.
This iterative approach allows you to calculate the LCM for any number of inputs.
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