Solve: Finding Positive Values for y = -1/6x² - 3⅓x

Question

Look at the following function:

y=16x2319x y=-\frac{1}{6}x^2-3\frac{1}{9}x

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

f(x) > 0

Step-by-Step Solution

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

  • Step 1: Identify the given equation in a standard form.
  • Step 2: Calculate the roots using the quadratic formula.
  • Step 3: Determine the sign of the function in different intervals determined by the roots.

Now, let's work through each step:

Step 1: The given quadratic function is y=16x2103x y = -\frac{1}{6}x^2 - \frac{10}{3}x . Here, a=16 a = -\frac{1}{6} , b=103 b = -\frac{10}{3} , and c=0 c = 0 .
We rewrite the function as y=16x2103x y = -\frac{1}{6}x^2 - \frac{10}{3}x .

Step 2: To find the roots of the quadratic equation, apply the quadratic formula:
x=b±b24ac2a x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}

Plugging in the values, we get:
x=(103)±(103)24(16)02(16) x = \frac{-(-\frac{10}{3}) \pm \sqrt{(-\frac{10}{3})^2 - 4 \cdot (-\frac{1}{6}) \cdot 0}}{2 \cdot (-\frac{1}{6})}
This simplifies to:
x=10313 x = \frac{\frac{10}{3}}{-\frac{1}{3}} (since the discriminant simplifies to zero as c c is zero)
x=0 x = 0 and x=1823 x = -18\frac{2}{3} (solving for the roots)

Step 3: Determining the intervals:
Because the parabola opens downwards (as a=16 a = -\frac{1}{6} is negative), the quadratic is positive between the roots.
Thus, f(x)>0 f(x) > 0 in the interval 1823<x<0 -18\frac{2}{3} < x < 0 .

Therefore, the solution to the problem is 1823<x<0 -18\frac{2}{3} < x < 0 .

Answer

-18\frac{2}{3} < x < 0