Thursday, November 15, 2018

Indeterminate form of infinity over 0?



I know that indeterminate forms exist in limits, such as 00, , 00, 0, 1.



Then, if limxap(x)= and limxaf(x)=0, can we call limxap(x)f(x) an indeterminate form of type 0? Or does it not exist since it has 0 for the denominator?


Answer




This is not an indeterminate form, because it's clear what happens. If f(x) approaches 0 from above, then the limit of p(x)f(x) is infinity. If f(x) approaches 0 from below, then the limit of p(x)f(x) is negative infinity. If f(x) keeps switching signs as it approaches zero, then the limit of the quotient fails to exist.



There's no "tug-of-war" here, like you have with indeterminate forms.


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