Question: Here are graphs of two equations in a system.
Determine if each of these systems could be represented by the graphs. Be prepared to explain how you know.
{ $x + 2y = 8$
$x = -5$ }
{ $y = -7x + 13$
$y = -1$ }
{ $3x = 8$
$3x + y = 15$ }
{ $y = 2x - 7$
$4 + y = 12$ }
Graph shapes: one descending straight line and one vertical line, intersecting at one point in the upper-middle/right area of the graph; position_hint = center.
1. **State the problem:** We need to determine which of the given systems of equations could be represented by a graph consisting of one descending straight line and one vertical line intersecting at one point.
2. **Recall the characteristics of lines:**
- A vertical line has an equation of the form $x = c$, where $c$ is a constant.
- A descending line has a negative slope.
3. **Analyze each system:**
**System 1:**
$$\begin{cases} x + 2y = 8 \\ x = -5 \end{cases}$$
- The second equation $x = -5$ is a vertical line.
- The first equation can be rewritten as $2y = 8 - x$ or $y = \frac{8 - x}{2}$.
- This is a line with slope $-\frac{1}{2}$ (since $y = -\frac{1}{2}x + 4$), which is descending.
- So system 1 has one vertical and one descending line.
**System 2:**
$$\begin{cases} y = -7x + 13 \\ y = -1 \end{cases}$$
- Both equations are in terms of $y$.
- The first is a descending line with slope $-7$.
- The second is a horizontal line $y = -1$.
- No vertical line here, so this system does not match the graph.
**System 3:**
$$\begin{cases} 3x = 8 \\ 3x + y = 15 \end{cases}$$
- The first equation is $x = \frac{8}{3}$, a vertical line.
- The second can be rewritten as $y = 15 - 3x$.
- This is a line with slope $-3$, which is descending.
- So system 3 matches the graph.
**System 4:**
$$\begin{cases} y = 2x - 7 \\ 4 + y = 12 \end{cases}$$
- The first equation has slope $2$, which is ascending.
- The second simplifies to $y = 8$, a horizontal line.
- No vertical line here, so this system does not match the graph.
4. **Conclusion:**
- Systems 1 and 3 could be represented by the described graph.
- Systems 2 and 4 could not.
5. **Final answer:**
- Yes: Systems 1 and 3
- No: Systems 2 and 4