Getting a sign chart for a function

In summary, the sign chart for the function $\frac{5(1-x)}{3x^{1/3}}$ is positive for $x < 0$, $x > 1$, and $0 < x < 1$, and negative for $0 < 1 < x$. The inflection points are at $x = 0$ and $x = 1$, where both the numerator and denominator equal zero. The radicand can be negative for odd roots, since the product of an odd number of negative numbers is negative.
  • #1
tmt1
234
0
I have the function

$$\frac{5(1-x)}{3x^{1/3}}$$

for which I need to find a sign chart. I know that for $x = 0$ and $x = 1$ are the inflection points, since those are the points for which the numerator and denominator will equal zero.

So, is the function positive or negative when $x < 0$, $x > 1$, and $0 < x < 1$?. I can get the values for when $x > 0$ easily enough, but what about when $x < 0$?

If I take $-1$, then
$$\frac{10}{3(-1)^{1/3}}$$

But I though for roots the radicand can't be negative?
 
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  • #2
Odd roots (not to be confused with the zeroes of a function) can be negative, since the product of an odd number of negative numbers is negative. :)
 
  • #3
The numerator, 5(1- x), is positive for x< 1 and negative for x> 1. The denominator, [tex]3x^{1/3}[/tex], is negative for x< 0 and positive for x> 0. A fraction is positive as long as both numerator and denominator have the same sigh, negative if they have different signs.

For x< 0< 1, the numerator is positive and the denominator is negative.

For 0< x< 1, the numerator is still positive and the denominator is positive.

For 0< 1< x, the numerator is negative and the denominator is positive.
 

FAQ: Getting a sign chart for a function

What is a sign chart for a function?

A sign chart for a function is a visual representation of the positive and negative intervals of a function. It is used to determine the behavior of a function and its roots or solutions.

How do I create a sign chart for a function?

To create a sign chart for a function, first identify the critical points of the function, where the function changes sign. Then, plot these points on a number line and test a value in each interval to determine the sign of the function in that interval.

Why is it important to have a sign chart for a function?

A sign chart helps in understanding the behavior of a function and its roots. It is useful in solving equations and inequalities involving the function, as well as identifying the maximum and minimum values of the function.

Can a sign chart be used for all types of functions?

Yes, a sign chart can be used for all types of functions, including polynomial, rational, exponential, and trigonometric functions. It is a universal tool for analyzing the behavior of functions.

Are there any shortcuts or tips for creating a sign chart quickly?

Yes, there are a few shortcuts and tips that can make creating a sign chart quicker and easier. These include factoring the function to identify its critical points, using a calculator to graph the function and identify the sign changes, and memorizing the sign patterns for different types of functions.

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