Domain Analysis: Finding Where (x-1/3)(-x-2¼) > 0

Find the positive and negative domains of the function:

$y=\left(x-\frac{1}{3}\right)\left(-x-2\frac{1}{4}\right)$

Determine for which values of $x$ the following is true:

$f(x) > 0$

To solve this problem, we'll follow these steps:

• Step 1: Identify the roots of the quadratic expression.
• Step 2: Determine the sign of each factor in intervals defined by these roots.
• Step 3: Identify where the product of these factors is positive.

Now, let's work through each step:

Step 1: Identify the roots.
The given function is $y = \left(x - \frac{1}{3}\right)\left(-x - 2\frac{1}{4}\right)$. To find the roots, solve each factor for zero:

• $x - \frac{1}{3} = 0$ gives $x = \frac{1}{3}$.
• $-x - 2\frac{1}{4} = 0$ gives $x = -2\frac{1}{4}$.

Step 2: Determine the sign of each factor in the intervals defined by these roots.
The zeros divide the x-axis into three intervals: $(-∞, -2\frac{1}{4})$, $(-2\frac{1}{4}, \frac{1}{3})$, and $(\frac{1}{3}, ∞)$.

Step 3: Test the signs and find where the product is positive.

• For $x < -2\frac{1}{4}$, test with $x = -3$: - $x - \frac{1}{3} = -3 - \frac{1}{3} < 0$ - $-x - 2\frac{1}{4} = 3 - 2\frac{1}{4} > 0$ - Product: Negative
• For $-2\frac{1}{4} < x < \frac{1}{3}$, test with $x = 0$: - $x - \frac{1}{3} = 0 - \frac{1}{3} < 0$ - $-x - 2\frac{1}{4} = 0 - 2\frac{1}{4} > 0$ - Product: Positive
• For $x > \frac{1}{3}$, test with $x = 1$: - $x - \frac{1}{3} = 1 - \frac{1}{3} > 0$ - $-x - 2\frac{1}{4} = -1 - 2\frac{1}{4} < 0$ - Product: Negative

Therefore, the solution to $f(x) > 0$ is in the interval:

$-2\frac{1}{4} < x < \frac{1}{3}$.