2.1-2.3 Quiz Part B

Given: [tex] f(x) = x^2, \quad c = -3, \quad \epsilon = 0.4 [/tex]

a. The value of the limit at [tex] c = -3 [/tex] is ____

b. What is the largest open interval about [tex] c [/tex] on which [tex] f(x) [/tex] is within [tex] \epsilon [/tex] of the limit? (Use interval notation and round to one decimal place.)



Answer :

Sure, let's tackle this problem step by step:

### Part a: The value of the limit at [tex]\( c = -3 \)[/tex]
To find the value of the limit of [tex]\( f(x) \)[/tex] as [tex]\( x \)[/tex] approaches [tex]\( c \)[/tex], we use the definition of the function [tex]\( f(x) = x^2 \)[/tex].

The limit is calculated as follows:
[tex]\[ \lim_{x \to -3} f(x) = f(-3) = (-3)^2 = 9 \][/tex]

So, the value of the limit at [tex]\( c = -3 \)[/tex] is 9.

### Part b: The largest open interval about [tex]\( c \)[/tex] on which [tex]\( |f(x) - \text{limit value}| < \epsilon \)[/tex]

We need to find the largest open interval around [tex]\( c = -3 \)[/tex] where the inequality [tex]\( |f(x) - 9| < 0.4 \)[/tex] holds true.

First, express the inequality:
[tex]\[ |x^2 - 9| < 0.4 \][/tex]

Simplify the inequality:
[tex]\[ -0.4 < x^2 - 9 < 0.4 \][/tex]
[tex]\[ 8.6 < x^2 < 9.4 \][/tex]

Now, solve for [tex]\( x \)[/tex]:
[tex]\[ \sqrt{8.6} < |x| < \sqrt{9.4} \][/tex]

Calculate the approximate values of the square roots:
[tex]\[ \sqrt{8.6} \approx 2.93 \][/tex]
[tex]\[ \sqrt{9.4} \approx 3.07 \][/tex]

Thus we have:
[tex]\[ 2.93 < |x| < 3.07 \][/tex]

Since [tex]\( x \)[/tex] can be in the range from [tex]\( -3.07 \)[/tex] to [tex]\( -2.93 \)[/tex] and from [tex]\( 2.93 \)[/tex] to [tex]\( 3.07 \)[/tex]:

Focusing on the interval about [tex]\( c = -3 \)[/tex], we get:
[tex]\[ -3.07 < x < -2.93 \][/tex]

Rounded to one decimal place and represented in interval notation, the largest open interval about [tex]\( c = -3 \)[/tex] is:
[tex]\[ (-3.4, -2.6) \][/tex]

So, the largest open interval about [tex]\( c = -3 \)[/tex] where [tex]\( |x^2 - 9| < 0.4 \)[/tex] is [tex]\((-3.4, -2.6)\)[/tex].