Vertex Sides
1. **State the problem:** We want to find values of $m$ such that the vertices of the parabolas
$$y=-x^2-4mx+m$$
and
$$y=x^2-2mx-1$$
both lie on the same side of the X-axis, meaning both their $y$-coordinates are either positive or negative.
2. **Find the vertex of the first parabola:** The general form is
$$y = ax^2 + bx + c$$
with $a=-1$, $b=-4m$, and $c=m$.
Vertex $x$-coordinate:
$$x_1 = -\frac{b}{2a} = -\frac{-4m}{2(-1)} = -\frac{-4m}{-2} = -2m$$
Calculate $y_1$:
$$y_1 = -(-2m)^2 -4m(-2m) + m = -4m^2 + 8m^2 + m = 4m^2 + m$$
3. **Find the vertex of the second parabola:**
Here $a=1$, $b=-2m$, $c=-1$.
Vertex $x$-coordinate:
$$x_2 = -\frac{b}{2a} = -\frac{-2m}{2} = m$$
Calculate $y_2$:
$$y_2 = (m)^2 - 2m(m) - 1 = m^2 - 2m^2 - 1 = -m^2 - 1$$
4. **Analyze sign conditions:**
- Vertex $y$-coordinate of first parabola: $$y_1 = 4m^2 + m$$
- Vertex $y$-coordinate of second parabola: $$y_2 = -m^2 - 1$$
Since $$y_2 = -m^2 -1 < 0$$ for all real $m$ (because $-m^2 \\leq 0$ and $-1$ makes it strictly negative), the second vertex is always below the X-axis.
5. **Both vertices on the same side means both $y_1$ and $y_2$ are negative:**
We require:
$$4m^2 + m < 0$$
6. **Solve inequality:**
$$4m^2 + m < 0$$
Factor out $m$:
$$m(4m + 1) < 0$$
The product is negative when the two factors have opposite signs:
- Case 1: $m < 0$ and $4m + 1 > 0$\Rightarrow $ $m > -\frac{1}{4}$
- Case 2: $m > 0$ and $4m + 1 < 0$ (impossible since $4m + 1 > 0$ if $m > 0$)
So the solution interval is:
$$-\frac{1}{4} < m < 0$$
7. **Check the multiple-choice points provided:**
Among the points $-\frac{1}{2}$, $-\frac{1}{4}$, $\frac{1}{2}$, and $\frac{1}{4}$, values inside $(-\frac{1}{4}, 0)$ include no exact options but the nearest point just inside is between $-\frac{1}{4}$ and $0$.
Thus, the vertex values lie on the same side of the X-axis (below) for:
$$m \in (-\frac{1}{4}, 0)$$
**Final answer:** $m$ values between $-\frac{1}{4}$ and $0$.