Analyze the Domains of a Quadratic Function: Unveiling Positive and Negative Realms

To find the positive and negative domains of the function $y = -x^2 + \frac{3}{2}x - \frac{21}{4}$, we first determine the roots of the equation:

Set $y = 0$, giving us:

$-x^2 + \frac{3}{2}x - \frac{21}{4} = 0$.

Using the quadratic formula $x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$, where $a = -1$, $b = \frac{3}{2}$, and $c = -\frac{21}{4}$, we calculate:

• First, compute the discriminant: $b^2 - 4ac = \left(\frac{3}{2}\right)^2 - 4(-1)\left(-\frac{21}{4}\right) = \frac{9}{4} - \frac{21}{1} = \frac{9}{4} - \frac{84}{4} = -\frac{75}{4}$.
• Since the discriminant is negative, the quadratic has no real roots.

This implies that the parabola does not intersect the $x$-axis and since the quadratic coefficient $a = -1$ is negative, the parabola opens downwards.

Thus, the function is always negative for all $x$. Therefore, the positive domain is empty, and the negative domain is the entire set of real numbers.

Conclusion: The solution to the problem is as follows:

$x < 0$: for all $x$

$x > 0$: none