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Find the interval(s) where the function is increasing and the interval(s) where it is decreasing. $$ h(x)=\frac{x^{2}}{x-1} $$

Short Answer

Expert verified
The function \(h(x) = \frac{x^2}{x-1}\) is increasing on the intervals \((-∞, 0)\) and \((2, +∞)\), and decreasing on the interval \((0, 1)\).

Step by step solution

01

Find the first derivative

Firstly, differentiate the given function \(h(x) = \frac{x^2}{x-1}\) with respect to x using the quotient rule. The quotient rule is given as: \(\frac{d}{dx}(\frac{u}{v}) = \frac{vu' - uv'}{v^2}\) Here, u = \(x^2\) and v = \(x - 1\). So, differentiate u with respect to x: \(u' = \frac{d}{dx}(x^2) = 2x\) And differentiate v with respect to x: \(v' = \frac{d}{dx}(x - 1) = 1\) Now, apply the quotient rule: \(h'(x) = \frac{(x - 1)(2x) - (x^2)(1)}{(x - 1)^2}\)
02

Simplify the first derivative

Now, simplify the expression of the first derivative: \(h'(x) = \frac{2x^2 - 2x - x^2}{(x - 1)^2}\) \(h'(x) = \frac{x^2 - 2x}{(x - 1)^2}\)
03

Find critical points

To find the critical points, we should equate the first derivative to zero and find when it is undefined. So, 1. Set the first derivative equal to zero: \(\frac{x^2 - 2x}{(x-1)^2} = 0\) Solve for x: \(x^2 - 2x = 0\) Factor out x: \(x(x - 2) = 0\) Thus, x = 0 and x = 2 are the critical points from the numerator. 2. Find where the first derivative is undefined: \((x - 1)^2 = 0\) Solve for x: x = 1 So, x = 1 is another critical point where the derivative is undefined.
04

Apply the first derivative test

Now, we have critical points x = 0, x = 1, and x = 2. We'll use the first derivative test to determine the intervals where the function is increasing and decreasing. For this, we'll test values in each of the intervals determined by the critical points. Intervals to test: - \(-∞ < x < 0\) - \(0 < x < 1\) - \(1 < x < 2\) - \(2 < x < +∞\) To perform the first derivative test, choose a representative value from each interval and plug it into the first derivative, \(h'(x)\): 1. Interval \(-∞ < x < 0\): Let x = -1 \(h'(-1) = \frac{(-1)^2 - 2(-1)}{(-1 - 1)^2} = \frac{3}{4}\) Since \(h'(-1) > 0\), the function is increasing in this interval. 2. Interval \(0 < x < 1\): Let x = 0.5 \(h'(0.5) = \frac{(0.5)^2 - 2(0.5)}{(0.5 - 1)^2} = -\frac{1}{4}\) Since \(h'(0.5) < 0\), the function is decreasing in this interval. 3. Interval \(1 < x < 2\): The first derivative is undefined at x = 1, so it's neither increasing nor decreasing. 4. Interval \(2 < x < +∞\): Let x = 3 \(h'(3) = \frac{(3)^2 - 2(3)}{(3 - 1)^2} = \frac{3}{4}\) Since \(h'(3) > 0\), the function is increasing in this interval.
05

Write the final answer

Based on the first derivative test results, the function is: - Increasing on the intervals \((-∞, 0)\) and \((2, +∞)\) - Decreasing on the interval \((0, 1)\) - Neither increasing nor decreasing at x = 1.

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Key Concepts

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

First Derivative Test
When investigating whether a function is increasing or decreasing at certain points, the first derivative test is an invaluable tool. It involves examining the first derivative of the function to determine the behavior around its critical points.

Let's break it down. A function is increasing when its slope (or derivative) is positive, and decreasing when the slope is negative. The critical points, which are the function's local highs and lows, occur where the derivative is zero or undefined. By testing points around these critical areas with the derivative, you can establish zones of increase and decrease.

For our function, we saw this method in action. By evaluating the sign of the derivative on either side of the critical points, we determined that the function h(x) is increasing when x is less than 0 and greater than 2, and decreasing when x is between 0 and 1. At x = 1, the derivative is undefined due to division by zero, indicating a vertical asymptote and undefined behavior in terms of increasing or decreasing.
Quotient Rule Differentiation
To find the rate of change of a function that is the ratio of two other functions, you'll want to employ the quotient rule for differentiation. It is succinctly expressed as: if you have a function which is the quotient of two functions u(x) and v(x), the derivative h'(x) is given by \(\frac{vu' - uv'}{v^2}\).

Let's use our exercise as an example, where we had the function h(x) = \frac{x^2}{x-1}. According to the quotient rule, we find the derivatives of the numerator u = x^2 and the denominator v = x - 1, denoted as u' and v' respectively. We then construct the derivative by following the rule: h'(x) = \frac{(x - 1)(2x) - (x^2)(1)}{(x - 1)^2}. By understanding and correctly applying the quotient rule, you can evaluate the behavior of the function at various points.
Critical Points
Identifying the critical points of a function is a crucial step in analyzing its graph. But what exactly are they? Critical points occur where the first derivative of a function is either zero or undefined, which typically indicate the peaks, troughs, or points where the tangent line is horizontal.

In our exercise, we found the critical points by setting the first derivative equal to zero and also by determining where the derivative does not exist. Through this process, we discovered that x = 0 and x = 2 are the points where the derivative is zero, indicating potential local extremum. Additionally, x = 1 is a point where our function’s first derivative does not exist, often suggesting a cusp or a vertical asymptote. Importantly, finding these critical points is not enough on their own; we must also examine the behavior of the function around these points, using, for example, the first derivative test, to fully understand their significance.

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