Question 767592
1. {{{1/9-1/7}}}
={{{((1*7)/(9*7))-((1*9)/(7*9))}}}
={{{7/63-9/63}}} 
={{{(7-9)/63}}}
={{{-2/63}}}
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2. {{{1/6-1/3}}}
={{{1/6-((1*2)/(3*2))}}}
={{{1/6-2/6}}}
={{{(1-2)/6}}}
={{{-1/6}}}