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Say whether l'Hospital's rule applies. If is does, use it to evaluate the given limit. If not, use some other method. $$ \lim _{x \rightarrow-\infty} \frac{2 x^{4}+20 x^{3}}{1000 x^{3}+6} $$

Short Answer

Expert verified
The given function is of the form ∞/∞ when x approaches -∞. Therefore, l'Hospital's rule applies. After applying l'Hospital's rule and evaluating the limit, we find that the limit of the given function is infinity: $$ \lim _{x \rightarrow-\infty} \frac{2 x^{4}+20 x^{3}}{1000 x^{3}+6} = \infty $$

Step by step solution

01

Check the form of the function as x approaches -∞

First, we will check the form of the function when x approaches -∞: $$ \frac{2 x^{4}+20 x^{3}}{1000 x^{3}+6} $$ As x approaches -∞, both \(x^{4}\) and \(x^{3}\) dominate the function, making other terms negligible.The function takes the form: $$ \lim _{x \rightarrow-\infty} \frac{2 x^{4}}{1000 x^{3}} $$ Since both the numerator and denominator go to ∞, the function is in the form ∞/∞ when x approaches -∞. Therefore, we can use l'Hospital's rule.
02

Applying l'Hospital's rule

Apply l'Hospital's rule by differentiating the numerator and the denominator: Numerator derivative: $$ \frac{d}{dx}(2 x^{4}+20 x^{3}) = 8 x^{3}+60 x^{2} $$ Denominator derivative: $$ \frac{d}{dx}(1000 x^{3}+6) = 3000 x^{2} $$ Now, compute the limit after applying l'Hospital's rule: $$ \lim _{x \rightarrow-\infty} \frac{8 x^{3}+60 x^{2}}{3000 x^{2}} $$
03

Evaluating the limit

As x approaches -∞, both \(x^{3}\) and \(x^{2}\) dominate the function, making other terms negligible. The function now takes the form: $$ \lim _{x \rightarrow-\infty} \frac{8 x^{3}}{3000 x^{2}} $$ Simplify this expression: $$ \lim _{x \rightarrow-\infty} \frac{8}{3000} x = -\frac{2}{750} x $$ Now, as x approaches -∞: $$ -\frac{2}{750}(-\infty) = \infty $$ So, the limit of the given function is infinity: $$ \lim _{x \rightarrow-\infty} \frac{2 x^{4}+20 x^{3}}{1000 x^{3}+6} = \infty $$

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Limits at Infinity
When studying calculus, you'll encounter various types of limits, one of them being limits at infinity. This concept refers to finding the value that a function approaches as the variable within that function tends toward positive or negative infinity. It's essential for understanding the behavior of functions over large scales.

Consider the example \( \frac{2 x^{4}+20 x^{3}}{1000 x^{3}+6} \) as \( x \to -\infty \) from the original exercise. To determine the limit at infinity, you simplify the function by focusing on the highest power terms in the numerator and denominator, since they will have the most significant impact on the function's value as \( x \to ±\infty \) . Here, this reasoning simplified the original expression to \( \frac{2 x^{4}}{1000 x^{3}} \) .

An understanding of limits at infinity is crucial for assessing the long-term behavior of functions, whether in mathematical modeling or in practical applications such as physics and engineering.
Calculus
Calculus is a branch of mathematics that deals with rates of change (differential calculus) and the accumulation of quantities (integral calculus). It's a powerful tool for analyzing and solving problems in the physical sciences, economics, computer science, engineering, and beyond. Calculus helps us understand and describe the dynamic world around us—everything from the rate at which a rocket gains altitude to the way light curves around a black hole.

In the textbook solution, calculus principles are used to evaluate a limit, where l'Hospital's rule—a specific technique within calculus—is applied to determine the limit of a rational function as \( x \to -\infty \) . Calculus is the mathematics of change, and limits are one of its foundational concepts, playing a pivotal role in defining and working with derivatives and integrals.
Derivative Calculus
Derivative calculus, often simply referred to as 'derivatives', concerns itself with understanding how a function changes as its input changes. The derivative of a function at a certain point is the slope of the tangent line to the function's graph at that point. It gives the rate at which the function's value is changing at that particular input value.

For example, in the solution to our exercise, derivatives of the numerator \( 8 x^{3}+60 x^{2} \) and the denominator \( 3000 x^{2} \) are computed as a part of applying l'Hospital's rule. This process involves taking the derivatives and then examining the limit to simplify the function. A solid grasp of derivatives is key to mastering calculus and progressing to more complex analyses of functions and their behaviors.

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Most popular questions from this chapter

The monthly sales of Sunny Electronics' new iSun walkman is given by \(q(t)=2,000 t-100 t^{2}\) units per month, \(t\) months after its introduction. The price Sunny charges is \(p(t)=100-t^{2}\) dollars per iSun, \(t\) months after introduction. Find the rate of change of monthly sales, the rate of change of the price, and the rate of change of monthly revenue six months after the introduction of the iSun. Interpret your answers. HINT [See Example 8(a).]

Calculate the derivatives of the functions in Exercises 1-46. HINT [See Example 1.] \(s(x)=\left(\frac{3 x-9}{2 x+4}\right)^{3}\)

Embryo Development Turkey embryos consume oxygen from the time the egg is laid through the time the chick hatches. For a brush turkey, the oxygen consumption (in milliliters) \(t\) days after the egg was laid can be approximated by \(^{27}\) \(C(t)=-0.0071 t^{4}+0.95 t^{3}-22 t^{2}+95 t . \quad(25 \leq t \leq 50)\) (An egg will typically hatch at around \(t=50\).) Suppose that at time \(t=0\) you have a collection of 100 newly laid eggs and that the number of eggs decreases linearly to zero at time \(t=50\) days. How fast is the total oxygen consumption of your collection of embryos changing after 40 days? (Round your answer to two significant digits.) Interpret the result. HINT [Total oxygen consumption \(=0\) xygen consumption per egg \(x\) Number of eggs.]

If f and g are functions of time, and at time t = 2, f equals 3 and is rising at a rate of 4 units per second, and g equals 5 and is rising at a rate of 6 units per second, then f/g equals ____ and is changing at a rate of ____ units per second.

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