Algebra I/Content/Working with Numbers/Subtracting Rational Numbers

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(Note to contributors: Please use the ^ symbol to designate exponents when you enter them in the wikibook. I will format them on the student-user interface.--HSTutorials 00:42, 17 July 2006 (UTC)

Vocabulary

Lesson

Subtracting fractions when the denominators are equal is also easy

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \frac{3}{7} - \frac{2}{7} = \frac{1}{7}}

Notice that when the denominators are the same for either adding or subtracting fractions we only add or subtract the numerators. With this in mind we can now use the techniques learned in Lesson 4 to subtract more complex fractions by finding the factors of the following fractions

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \frac{121}{456} - \frac{61}{570} = \frac{11 \times 11}{2 \times 2 \times 2 \times 3 \times 19} - \frac{61}{2 \times 3 \times 5 \times 19}}

We can now see that multiplying 456 by 5 and 570 by 4 gives the smallest possible denominator

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \frac{121 \times 5}{5 \times 456} - \frac{4 \times 61}{4 \times 570} = \frac{605 - 244}{2280} = \frac{361}{2280}}

Now the question is is this fraction irreducible? We know the factors in the denominator so checking if 361 is divisible by the numbers 2, 3, 5, 19 will show that 361/19 = 19 therefore

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \frac{361}{2280} = \frac{19}{120}}

Which is now an irreducible fraction.

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