2 simple rule for fraction

Question

I am embarassed to ask this question, but when a fraction divides a number, the rule is:

$\dfrac{a}{\dfrac{b}{c}}$ it is supposed to be $\dfrac{a\cdot c}{b}$

$\dfrac{\dfrac{a}{b}}{c}$ it is supposed to be $\dfrac{a}{b\cdot c}$

Notice the bar for diving fraction is different, in the first fraction it is longer for $a$ and $b$, while in the second it is longer for $b$ and $c$

So which rule should I use? I thought division of a number means multiplying the inverse of that number, am I correct?

Writing such a thing, whose interpretation is based on millimetre differences in bar-length, is an abomination. If you really must, then write $$\frac{a}{b/c}$$ etc. — Angina Seng, Nov 30 '19 at 04:59

Ross Millikan · Answer 1 · 2019-11-30T05:13:32.293

1

The longer bar means there are parentheses around the stuff above and below. So $$\dfrac {\dfrac ab}{\dfrac cd}=\dfrac {\left(\frac ab\right)}{\left(\frac cd\right)}=\frac{ad}{bc}$$ where the middle bar is supposed to be longer in the first fraction.

edited Nov 30 '19 at 05:13

answered Nov 30 '19 at 05:01

Ross Millikan

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2 simple rule for fraction

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