Post

Created by @nathanedwards
 at November 1st 2023, 3:46:16 pm.

AP Calculus AB Exam Question:

Let f(x) be a continuous function defined on the closed interval [a, b], where a < b. Determine the limit of the function as x approaches c, where c is a real number within the interval (a, b), using the ϵ\epsilon-δ\delta definition of a limit.

Consider the function:

f(x)={x2if xccx+2if x>c f(x) = \begin{cases} x^2 & \text{if } x \leq c \\ cx + 2 & \text{if } x > c \end{cases}

Using the ϵ\epsilon-δ\delta definition of a limit, determine the following limit:

limxcf(x) \lim_{x \to c} f(x)

Step-by-Step Solution:

To find the limit as x approaches c, we will employ the ϵ\epsilon-δ\delta definition of a limit, which states:

For a given value ϵ>0\epsilon > 0, there exists a value δ>0\delta > 0 such that if 0<xc<δ0 < |x - c| < \delta, then f(x)L<ϵ|f(x) - L| < \epsilon, where L is the desired limit.

First, let's analyze the behavior of the function on the left and right sides of c.

For x values less than or equal to c:

f(x)=x2 f(x) = x^2

For x values greater than c:

f(x)=cx+2 f(x) = cx + 2

Now, let's find the limit of f(x) as x approaches c from the left side.

limxcf(x)=limxcx2=c2 \lim_{x \to c^-} f(x) = \lim_{x \to c^-} x^2 = c^2

Similarly, let's find the limit of f(x) as x approaches c from the right side.

limxc+f(x)=limxc+cx+2=cc+2=c2+2 \lim_{x \to c^+} f(x) = \lim_{x \to c^+} cx + 2 = c \cdot c + 2 = c^2 + 2

Next, let's combine both limits:

limxcf(x)=limxcf(x)=limxc+f(x)=c2 \lim_{x \to c} f(x) = \lim_{x \to c^-} f(x) = \lim_{x \to c^+} f(x) = c^2

Therefore, the limit of the given function as x approaches c is limxcf(x)=c2 \lim_{x \to c} f(x) = c^2 .