Domain Analysis: Solve (x+1/6)(-x-4/9) > 0 Step by Step

Question

Find the positive and negative domains of the function below:

y=(x+16)(x419) y=\left(x+\frac{1}{6}\right)\left(-x-4\frac{1}{9}\right)

Then determine for which values of x x the following is true:

f\left(x\right) > 0

Step-by-Step Solution

To solve this problem, we will determine where the function, given as y=(x+16)(x419) y = \left(x + \frac{1}{6}\right)\left(-x - 4\frac{1}{9}\right) , is positive.

Step 1: **Find the Roots**
Set the function equal to zero: (x+16)(x419)=0 \left(x + \frac{1}{6}\right)\left(-x - 4\frac{1}{9}\right) = 0 . This yields:
- x+16=0 x + \frac{1}{6} = 0 which gives x=16 x = -\frac{1}{6} , and
- x419=0 -x - 4\frac{1}{9} = 0 which gives x=419 x = -4\frac{1}{9} .
Thus, the roots are x=16 x = -\frac{1}{6} and x=419 x = -4\frac{1}{9} .

Step 2: **Analyze Sign Intervals**
The parabola opens downwards because the product has a negative coefficient as the leading term.
We have intervals: x<419 x < -4\frac{1}{9} , 419<x<16 -4\frac{1}{9} < x < -\frac{1}{6} , and x>16 x > -\frac{1}{6} .

Since the quadratic opens downwards, it is positive between the roots (-4\frac{1}{9}, -\frac{1}{6}), where f(x)>0 f(x) > 0 .

Therefore, the solution for the values of x x for which f(x)>0 f(x) > 0 is:

419<x<16 -4\frac{1}{9} < x < -\frac{1}{6}

Answer

-4\frac{1}{9} < x < -\frac{1}{6}