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Suppose that [tex]\(\lim _{x \rightarrow 3} f(x)=4\)[/tex] and [tex]\(\lim _{x \rightarrow 3} g(x)=-7\)[/tex]. Find the following limits:

a. [tex]\(\lim _{x \rightarrow 3}[f(x) g(x)]\)[/tex]

b. [tex]\(\lim _{x \rightarrow 3}[3 f(x) g(x)]\)[/tex]

c. [tex]\(\lim _{x \rightarrow 3}[f(x)+8 g(x)]\)[/tex]

d. [tex]\(\lim _{x \rightarrow 3}\left[\frac{f(x)}{f(x)-g(x)}\right]\)[/tex]

[tex]\[
\lim _{x \rightarrow 3}[f(x) g(x)] = \square
\][/tex]

(Simplify your answer.)


Sagot :

Let's solve these limit problems step-by-step:

Given:
[tex]\[ \lim_{x \to 3} f(x) = 4 \quad \text{and} \quad \lim_{x \to 3} g(x) = -7 \][/tex]

### Part (a)
[tex]\[ \lim_{x \to 3} [f(x) g(x)] \][/tex]

Using the limit property that states [tex]\(\lim_{x \to a} [f(x) \cdot g(x)] = \left(\lim_{x \to a} f(x)\right) \cdot \left(\lim_{x \to a} g(x)\right)\)[/tex], we have:
[tex]\[ \lim_{x \to 3} [f(x) g(x)] = \left(\lim_{x \to 3} f(x)\right) \cdot \left(\lim_{x \to 3} g(x)\right) = 4 \cdot (-7) = -28 \][/tex]

So,
[tex]\[ \lim_{x \to 3} [f(x) g(x)] = -28 \][/tex]

### Part (b)
[tex]\[ \lim_{x \to 3} [3 f(x) g(x)] \][/tex]

We can factor out the constant 3 from the limit:
[tex]\[ \lim_{x \to 3} [3 f(x) g(x)] = 3 \cdot \lim_{x \to 3} [f(x) g(x)] \][/tex]

From part (a), we know:
[tex]\[ \lim_{x \to 3} [f(x) g(x)] = -28 \][/tex]

So,
[tex]\[ \lim_{x \to 3} [3 f(x) g(x)] = 3 \cdot (-28) = -84 \][/tex]

### Part (c)
[tex]\[ \lim_{x \to 3} [f(x) + 8 g(x)] \][/tex]

Using the limit property that states [tex]\(\lim_{x \to a} [f(x) + g(x)] = \left(\lim_{x \to a} f(x)\right) + \left(\lim_{x \to a} g(x)\right)\)[/tex], we have:
[tex]\[ \lim_{x \to 3} [f(x) + 8 g(x)] = \lim_{x \to 3} f(x) + 8 \cdot \lim_{x \to 3} g(x) \][/tex]

Given,
[tex]\[ \lim_{x \to 3} f(x) = 4 \quad \text{and} \quad \lim_{x \to 3} g(x) = -7 \][/tex]

So,
[tex]\[ \lim_{x \to 3} [f(x) + 8 g(x)] = 4 + 8 \cdot (-7) = 4 + (-56) = 4 - 56 = -52 \][/tex]

### Part (d)
[tex]\[ \lim_{x \to 3} \left[\frac{f(x)}{f(x) - g(x)}\right] \][/tex]

Using the limit properties and given:
[tex]\[ \lim_{x \to 3} f(x) = 4 \quad \text{and} \quad \lim_{x \to 3} g(x) = -7 \][/tex]

First, we find the limit of the denominator:
[tex]\[ \lim_{x \to 3} [f(x) - g(x)] = \lim_{x \to 3} f(x) - \lim_{x \to 3} g(x) = 4 - (-7) = 4 + 7 = 11 \][/tex]

Since the denominator does not approach zero, we can use the limit properties for division:
[tex]\[ \lim_{x \to 3} \left[\frac{f(x)}{f(x) - g(x)}\right] = \frac{\lim_{x \to 3} f(x)}{\lim_{x \to 3} [f(x) - g(x)]} = \frac{4}{11} \][/tex]

So, we have:
[tex]\[ \lim_{x \to 3} \left[\frac{f(x)}{f(x) - g(x)}\right] = \frac{4}{11} \approx 0.36363636363636365 \][/tex]

### Summary
[tex]\[ \begin{aligned} \lim_{x \to 3} [f(x) g(x)] &= -28, \\ \lim_{x \to 3} [3 f(x) g(x)] &= -84, \\ \lim_{x \to 3} [f(x) + 8 g(x)] &= -52, \\ \lim_{x \to 3} \left[\frac{f(x)}{f(x) - g(x)}\right] &\approx 0.36363636363636365. \end{aligned} \][/tex]

Thus, the answers are:

a. [tex]\(-28\)[/tex]

b. [tex]\(-84\)[/tex]

c. [tex]\(-52\)[/tex]

d. [tex]\(\approx 0.3636\)[/tex]