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From Förberedande kurs i matematik 1

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We divide up the two numerators into the smallest possible integer factors,
\displaystyle \begin{align}
& 12=2\centerdot 6=2\centerdot 2\centerdot 3 \\
& 14=2\centerdot 7 \\
\end{align}
The expression can thus be written as
\displaystyle \frac{1}{2\centerdot 2\centerdot 3}-\frac{1}{2\centerdot 7}
Here, we see that the denominators have a factor \displaystyle 2 in common. We multiply the top and bottom of the first fraction by \displaystyle 7 and the second by \displaystyle 2\centerdot 3 i.e. we leave out the common factor \displaystyle 2 , so that the fractions have the lowest common denominator \displaystyle 2\centerdot 2\centerdot 3\centerdot 7 ,
\displaystyle \frac{1}{12}-\frac{1}{14}=\frac{1}{2\centerdot 2\centerdot 3}-\frac{1}{2\centerdot 7}=\frac{1}{2\centerdot 2\centerdot 3}\centerdot \frac{7}{7}-\frac{1}{2\centerdot 7}\centerdot \frac{2\centerdot 3}{2\centerdot 3}
The lowest common denominator is \displaystyle 84 .
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(current) | 09:59, 26 March 2008 | Lina (Talk | contribs) | 420×622 | 46 KB |
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