1. Mar 1, 2009

### smh745

1.the qustion is proof by contradiction is in the jpg file

2. the format of the solution is in the attachement doc.

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2. Mar 1, 2009

### HallsofIvy

Staff Emeritus
The FORMAT of the solution is to be as given in that "Word" file? Since you want to prove "not a" by contradiction, start with its contradiction: "not(not a)= a". Then see what follows from "a". For example, you are given "(not d) or c implies (not a)". The contrapositive of that is "a implies not((not d) or c)" which is the same as "a implies (d and (not c)"