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Homework Statement
Let ##n\in N ##. Prove that if ##|n-1|+|n+1|\leq 1,## then ## |n^{2}-1|\leq 4##
Homework Equations
The Attempt at a Solution
I am trying to show by a counter example that this statement is not true.
Consider this statement:
##|n-1|+|n+1| \leq 1##
Assume :
|n-1|=n-1 >0 and |n+1|=n+1>0
Then, by our former statement, ## n-1+n+1 \leq 1,##
which gives
## 2n \leq 1 , \text{where n} \in N##
Now, divide by 2, and ##n \leq \dfrac{1}{2}##, which is not possible since ##n \in N##
Call ##|n-1|+|n+1| \leq 1## , P.
In logic, P→Q. If P is false, then Q does not matter, the implication is always true.
Is this non-elegant proof correct?