Wize High School Grade 12 Calculus Textbook > Rate of Change

Evaluating 00\frac{0}{0} Limits -- with Absolute Values

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Example: Absolute Value 0/0 Limits

limx1x1x21=\displaystyle\lim _{x\rightarrow1^-}\frac{\left|x-1\right|}{x^2-1}=

Direct substitution gives us 00\frac{0}{0}.

As x1x\rightarrow1^-, x1x-1 is negative, so x1=(x1)\left|x-1\right|=-\left(x-1\right).
Let's rewrite the limit without absolute values.
limx1x1x21\displaystyle\lim _{x\rightarrow1^-}\frac{\left|x-1\right|}{x^2-1}
=limx1(x1)x21=\displaystyle\lim _{x\rightarrow1^-}\frac{-(x-1)}{x^2-1}
=limx1(x1)(x1)(x+1)=\displaystyle\lim _{x\rightarrow1^-}\frac{-(x-1)}{(x-1)(x+1)}
=limx11x+1=\displaystyle\lim_{x\to1^-}-\frac{1}{x+1}
=12=-\frac{1}{2}

Practice: Absolute Value 0/0 Limits

limx0 32x2x3x=\displaystyle\lim_{x\to0}\ \frac{\left|3-2x\right|-\left|2x-3\right|}{x}=

Practice: Absolute Value 0/0 Limits

Evaluate limx2 x25x10\displaystyle\lim_{x\to2}\ \frac{x-2}{|5x-10|}, if it exists.