Algebra I and above  This is a history lesson.  Students would ask why we were rationalizing the denominator.  First I answered that it was considered better form.  But I was dissatisfied by my own response.  I started asking my fellow teachers and they knew of no other reason.  I started to reflect my experience and realized that the answer came when approximated expressions involving irrational numbers.  I am old to remember doing this by hand.  The answer became obvious, the computations were easier with the radical in the numerator.
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