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Exercise 7.5.3 (Every convergent is a good approximation)
Say that a rational number with is a “good approximation” to the irrational number if
where, as indicated, the minimum on the right is to be taken over all pairs of integers satisfying . Prove that every convergent to with is a “good approximation”.
Answers
Proof. By the first assertion in Theorem 7.13, if , where and , then . Hence, if ,
So every convergent to with is a “good approximation” to . □