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1.3 Prove that [tex]1.\dot{3}[/tex] is a rational number.

Sagot :

To prove that [tex]\(1.\overline{331}\)[/tex] is a rational number, we proceed as follows:

1. Define the repeating decimal:

Let [tex]\( x = 1.\overline{331} \)[/tex]. This notation means that the sequence "331" repeats infinitely after the decimal point.

2. Shift the decimal point to the right three places:

Since the repeating part has 3 digits, we multiply [tex]\( x \)[/tex] by [tex]\(1000\)[/tex]:

[tex]\[ 1000x = 1331.\overline{331} \][/tex]

3. Set up the equation to eliminate the repeating decimal:

Now, we have two equations:
[tex]\[ x = 1.\overline{331} \quad \text{(Equation 1)} \][/tex]
[tex]\[ 1000x = 1331.\overline{331} \quad \text{(Equation 2)} \][/tex]

By subtracting Equation 1 from Equation 2, we eliminate the repeating part:
[tex]\[ 1000x - x = 1331.\overline{331} - 1.\overline{331} \][/tex]

4. Simplify the subtraction:

On the left side we have:
[tex]\[ 1000x - x = 999x \][/tex]
On the right side we have:
[tex]\[ 1331.\overline{331} - 1.\overline{331} = 1330 \][/tex]

Therefore:
[tex]\[ 999x = 1330 \][/tex]

5. Solve for [tex]\( x \)[/tex]:

To find [tex]\( x \)[/tex], divide both sides by 999:
[tex]\[ x = \frac{1330}{999} \][/tex]

6. Simplify the fraction:

To confirm that [tex]\(\frac{1330}{999}\)[/tex] is in its simplest form, we can check for common factors. Both the numerator and the denominator can be divided by their greatest common divisor (GCD), which is 1 in this case:

[tex]\[ \frac{1330}{999} = \text{simplifies to} \frac{1330}{999} \][/tex]

Notice that the fraction is already in its simplest form; it does not simplify further.

Therefore, [tex]\(1.\overline{331} = \frac{1330}{999}\)[/tex], proving that [tex]\(1.\overline{331}\)[/tex] is a rational number because it can be expressed as a ratio of two integers.

By transforming a repeating decimal into a fraction, we've shown explicitly that [tex]\(1.\overline{331}\)[/tex] is indeed rational.