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2013-03-21T08:31:35+01:00

a/b = (-2/21) /( 5/-7) = (2/21) *(7/5) =2/15

 

b/a =( 5/-7) / (-2/21) =(5/7)*(21/2) =15/2

 

a*b =(-2/21) *( 5/-7) = (2*5)/(7*21) =10/147

 

a -b=(-2/21) -( 5/-7) = -2/21    +  5/7  =  -2/21   +  15/21 =  13/21