Question 1143269
3/4-1/2
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For problems like this with 2 terms:
{{{a/b - c/d = (ad - bc)/bd}}}
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---> {{{(3*2 - 4*1)/(4*2) = (6-4)/8 = 2/8 = 1/4}}}
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I remember the LCD, Least Common Denominator from grade school.
It's a waste of time.
It's not relevant to this example, but is for some other problems.
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For example:
{{{3/4 + 1/3 + 5/6}}}
The LCD is 12, but there's no good reason to waste time finding it.
Use the product of the 3 DENs': 4*3*6 = 72
--> {{{54/72 + 24/72 + 60/72 = 138/72}}}
Then reduce.
= {{{23/12}}}
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Another example:
{{{4/a + b/c + 5/ac}}}
Use the product:  {{{a*c*ac = a^2c^2}}}
---> {{{(4ac^2 + b*a^2c + 5ac)/a^2c^2}}}
= {{{(4ac^2 + a^2bc + 5ac)/a^2c^2}}}
= {{{(4ac + a^2b + 5a)/a^2c}}}
= {{{(4c + ab + 5)/ac}}}
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Using the product and reducing the result takes less time than finding the LCD in most cases.
IDK why schools and texts persist with the LCD.