Line Equations 65A9A7
1. **State the problem:**
We have two lines, $D_1$ and $D_2$. We know $D_1$ cuts the y-axis at $(0, -5)$ and is parallel to $D_2$ given by $x - 2y - 1 = 0$. We also know $D_1$ cuts the x-axis at $(-2, 0)$ and is perpendicular to another $D_2$ given by $3x - 2y + 1 = 0$. We need to find the equations of these lines.
2. **Find the equation of $D_1$ parallel to $D_2: x - 2y - 1 = 0$**
- The slope of $D_2$ is found by rewriting it in slope-intercept form:
$$x - 2y - 1 = 0 \implies -2y = -x + 1 \implies y = \frac{1}{2}x - \frac{1}{2}$$
- So slope $m = \frac{1}{2}$.
- Since $D_1$ is parallel to $D_2$, $D_1$ has the same slope $m = \frac{1}{2}$.
- $D_1$ cuts the y-axis at $(0, -5)$, so the y-intercept $b = -5$.
- Equation of $D_1$ is:
$$y = \frac{1}{2}x - 5$$
3. **Find the equation of $D_1$ perpendicular to $D_2: 3x - 2y + 1 = 0$**
- Find slope of $D_2$:
$$3x - 2y + 1 = 0 \implies -2y = -3x - 1 \implies y = \frac{3}{2}x + \frac{1}{2}$$
- Slope of $D_2$ is $m_2 = \frac{3}{2}$.
- Slope of $D_1$ perpendicular to $D_2$ is the negative reciprocal:
$$m_1 = -\frac{1}{m_2} = -\frac{1}{\frac{3}{2}} = -\frac{2}{3}$$
- $D_1$ cuts the x-axis at $(-2, 0)$, so point $(-2, 0)$ lies on $D_1$.
- Use point-slope form:
$$y - y_1 = m(x - x_1)$$
$$y - 0 = -\frac{2}{3}(x - (-2)) = -\frac{2}{3}(x + 2)$$
- Simplify:
$$y = -\frac{2}{3}x - \frac{4}{3}$$
**Final answers:**
- Equation of $D_1$ parallel to $D_2 \equiv x - 2y - 1 = 0$ is:
$$y = \frac{1}{2}x - 5$$
- Equation of $D_1$ perpendicular to $D_2 \equiv 3x - 2y + 1 = 0$ is:
$$y = -\frac{2}{3}x - \frac{4}{3}$$