Post

Created by @nathanedwards
 at November 3rd 2023, 7:53:38 pm.

Question:

Find the limit algebraically:

limx4x216x+4 \lim_{x \to -4} \frac{x^2 - 16}{x+4}

Answer:

To find the limit of the given expression, we can plug in the value that xx is approaching and see what we get. However, when we substitute x=4x = -4 directly into the expression, we encounter an indeterminate form of 00\frac{0}{0}.

Therefore, instead of performing direct substitution, we can use algebraic manipulation in order to simplify the expression and find the limit.

Step 1: Factorize the numerator as the difference of squares:

x216=(x+4)(x4) x^2 - 16 = (x + 4)(x - 4)

Step 2: Rewrite the expression:

x216x+4=(x+4)(x4)x+4 \frac{x^2 - 16}{x + 4} = \frac{(x + 4)(x - 4)}{x + 4}

Step 3: Cancel out the common factor of x+4x + 4:

(x+4)(x4)x+4=x4 \frac{(x + 4)(x - 4)}{x + 4} = x - 4

Now, we can take the limit as xx approaches 4-4 of the simplified expression:

limx4x216x+4=limx4(x4) \lim_{x \to -4} \frac{x^2 - 16}{x + 4} = \lim_{x \to -4} (x - 4)

Since we have eliminated the indeterminate form, we can now plug in x=4x = -4 directly into the expression:

limx4(x4)=(4)4=8 \lim_{x \to -4} (x - 4) = (-4) - 4 = -8

Therefore, the limit of the given expression as xx approaches 4-4 is 8-8.