1. 7<x<13
The range for 1/x would be from 1/13 to 1/7, the reciprocals of 7 and 13.
answer: 1/13<1/x<1/7
2. 6<a<10 -----> -10<-a<-6 -------> -8<2-a<-4
×-1 +2
answer: -8<2-a<-4
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