- #1
thelannonmonk
- 7
- 0
1. Let m, n, p, q [itex]\in[/itex] Z
If 0 < m < n and 0< p [itex]\leq[/itex] q, then mp < nq
2. Propositions/axioms I can use that relate to inequalities
2.4 Let m,n,p [itex]\in[/itex] Z. If m < n and n < p, then m < p
2.5 For each n [itex]\in[/itex] N there exists an m [itex]\in[/itex] N such that m > n
2.6 Let m,n [itex]\in[/itex] Z. If m [itex]\leq[/itex] n [itex]\leq[/itex] m then m=n
2.7 i)If m < n, then m+p < n+p
2.7 ii)If m < n and p < q then m+p < n+q
So far, my first idea is to say if m < n, then sm < sn (s being an arbitrary integer). However, I don't have an axiom or proposition to reference for this step, so I don't even know if I can use it. If I could use it, then i would go on to say that if sm < sn, then if p<q, then pm<qn, but this is the thing they want me to prove! So I can't reference the proposition I am trying to prove, I am just stuck!
The other issue is that I can only use axioms an propositions from earlier in the book, so my options are limited, but the most obviously useful ones seem to be 2.7 (i) and (ii)
If 0 < m < n and 0< p [itex]\leq[/itex] q, then mp < nq
2. Propositions/axioms I can use that relate to inequalities
2.4 Let m,n,p [itex]\in[/itex] Z. If m < n and n < p, then m < p
2.5 For each n [itex]\in[/itex] N there exists an m [itex]\in[/itex] N such that m > n
2.6 Let m,n [itex]\in[/itex] Z. If m [itex]\leq[/itex] n [itex]\leq[/itex] m then m=n
2.7 i)If m < n, then m+p < n+p
2.7 ii)If m < n and p < q then m+p < n+q
The Attempt at a Solution
So far, my first idea is to say if m < n, then sm < sn (s being an arbitrary integer). However, I don't have an axiom or proposition to reference for this step, so I don't even know if I can use it. If I could use it, then i would go on to say that if sm < sn, then if p<q, then pm<qn, but this is the thing they want me to prove! So I can't reference the proposition I am trying to prove, I am just stuck!
The other issue is that I can only use axioms an propositions from earlier in the book, so my options are limited, but the most obviously useful ones seem to be 2.7 (i) and (ii)
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