Post

Created by @nathanedwards
 at November 1st 2023, 11:56:05 am.

Question:

Find the limit algebraically:

limx2x38x24x\lim_{{x \to 2}} \frac{{x^3 - 8}}{{x^2 - 4x}}

Answer:

To find the limit algebraically, we can attempt direct substitution by plugging in x=2x=2 into the expression:

limx2(2)38(2)24(2)\lim_{{x \to 2}} \frac{{(2)^3 - 8}}{{(2)^2 - 4(2)}}

However, direct substitution results in an indeterminate form of 00\frac{0}{0}. This suggests that we need to manipulate the expression in order to simplify it and find the limit.

Factoring the numerator and denominator, we have:

limx2(x2)(x2+2x+4)x(x4)\lim_{{x \to 2}} \frac{{(x-2)(x^2+2x+4)}}{{x(x-4)}}

Now, we can cancel out the common factor of (x2)(x-2):

limx2(x2)(x2+2x+4)x(x4)=limx2x2+2x+4x(x4)\lim_{{x \to 2}} \frac{{\cancel{(x-2)}(x^2+2x+4)}}{{x(x-4)}} = \lim_{{x \to 2}} \frac{{x^2+2x+4}}{{x(x-4)}}

We still have an indeterminate form of 00\frac{0}{0}, so we need to further simplify the expression. We can do this by factoring the quadratic in the numerator:

limx2(x+2)(x+2)x(x4)\lim_{{x \to 2}} \frac{{(x+2)(x+2)}}{{x(x-4)}}

Now, we can cancel out the common factors of (x+2)(x+2):

limx2(x+2)(x+2)x(x4)=limx2x+2x4\lim_{{x \to 2}} \frac{{\cancel{(x+2)}(x+2)}}{{x(x-4)}} = \lim_{{x \to 2}} \frac{{x+2}}{{x-4}}

Finally, we can substitute x=2x=2 into the simplified expression:

limx22+224=limx2(2)=2\lim_{{x \to 2}} \frac{{2+2}}{{2-4}} = \lim_{{x \to 2}} (-2) = \boxed{-2}

Therefore, the limit of x38x24x\frac{{x^3 - 8}}{{x^2 - 4x}} as xx approaches 22 is 2-2.