Answer
To graph the equations \(4x + y = 8\), \(x + 4y = 8\), and \(x + y = 2\), follow these steps:
1. **Convert each equation to slope-intercept form:**
- \(4x + y = 8\) becomes \(y = 8 - 4x\).
- \(x + 4y = 8\) becomes \(y = 2 - \frac{x}{4}\).
- \(x + y = 2\) becomes \(y = 2 - x\).
2. **Find the intercepts for each line:**
- For \(4x + y = 8\): intercepts at \((0,8)\) and \((2,0)\).
- For \(x + 4y = 8\): intercepts at \((0,2)\) and \((8,0)\).
- For \(x + y = 2\): intercepts at \((0,2)\) and \((2,0)\).
3. **Plot the intercepts on a coordinate plane and draw each line through them.**
4. **Identify the intersection points:**
- \(x + y = 2\) and \(x + 4y = 8\) intersect at \((0,2)\).
- \(x + y = 2\) and \(4x + y = 8\) intersect at \((2,0)\).
- \(4x + y = 8\) and \(x + 4y = 8\) intersect at \(\left(\frac{8}{5}, \frac{8}{5}\right)\).
By following these steps, you can accurately graph the three equations and locate their intersection points.
Solution
**Step 1. Rewrite each equation in slope-intercept form.**
1. For \(4x + y = 8\):
- Solve for \(y\):
\[
y = 8 - 4x
\]
- **Intercepts:**
- When \(x = 0\): \(y = 8\) \(\rightarrow (0,8)\).
- When \(y = 0\): \(0 = 8 - 4x \Rightarrow 4x = 8 \Rightarrow x = 2\) \(\rightarrow (2,0)\).
2. For \(x + 4y = 8\):
- Solve for \(y\):
\[
4y = 8 - x \quad \Rightarrow \quad y = 2 - \frac{x}{4}
\]
- **Intercepts:**
- When \(x = 0\): \(y = 2\) \(\rightarrow (0,2)\).
- When \(y = 0\): \(0 = 2 - \frac{x}{4} \Rightarrow \frac{x}{4} = 2 \Rightarrow x = 8\) \(\rightarrow (8,0)\).
3. For \(x + y = 2\):
- Solve for \(y\):
\[
y = 2 - x
\]
- **Intercepts:**
- When \(x = 0\): \(y = 2\) \(\rightarrow (0,2)\).
- When \(y = 0\): \(0 = 2 - x \Rightarrow x = 2\) \(\rightarrow (2,0)\).
---
**Step 2. Plot the Points and Draw the Lines**
1. **Graph of \(4x + y = 8\):**
- Plot the intercepts \((0,8)\) and \((2,0)\).
- Draw a straight line through these points.
- The line has a slope \(-4\).
2. **Graph of \(x + 4y = 8\):**
- Plot the intercepts \((0,2)\) and \((8,0)\).
- Draw a straight line through these points.
- The line has a slope of \(-\frac{1}{4}\).
3. **Graph of \(x + y = 2\):**
- Plot the intercepts \((0,2)\) and \((2,0)\).
- Draw a straight line through these points.
- The line has a slope of \(-1\).
---
**Step 3. Verify the Intersection Points**
1. **Intersection of \(x + y = 2\) and \(x + 4y = 8\):**
- From \(x+y=2\), express \(x\) as:
\[
x = 2 - y
\]
- Substitute into \(x + 4y = 8\):
\[
(2 - y) + 4y = 8 \quad \Rightarrow \quad 2 + 3y = 8 \quad \Rightarrow \quad 3y = 6 \quad \Rightarrow \quad y = 2
\]
- Substitute \(y = 2\) into \(x = 2 - y\):
\[
x = 2 - 2 = 0
\]
- Intersection point is \((0,2)\).
2. **Intersection of \(x + y = 2\) and \(4x + y = 8\):**
- From \(x+y=2\), express \(y\) as:
\[
y = 2 - x
\]
- Substitute into \(4x + y = 8\):
\[
4x + (2 - x) = 8 \quad \Rightarrow \quad 3x + 2 = 8 \quad \Rightarrow \quad 3x = 6 \quad \Rightarrow \quad x = 2
\]
- Then, \(y = 2 - 2 = 0\).
- Intersection point is \((2,0)\).
3. **Intersection of \(4x + y = 8\) and \(x + 4y = 8\):**
- We already have two intersections from above with the third line, but we find this intersection as well.
- Solve the system:
\[
\begin{cases}
4x + y = 8 \\
x + 4y = 8
\end{cases}
\]
- Multiply the second equation by 4:
\[
4x + 16y = 32
\]
- Subtract the first equation \( (4x+y=8) \) from this:
\[
(4x + 16y) - (4x + y) = 32 - 8 \quad \Rightarrow \quad 15y = 24 \quad \Rightarrow \quad y = \frac{24}{15} = \frac{8}{5}
\]
- Substitute \( y = \frac{8}{5} \) into \(4x + y = 8\):
\[
4x + \frac{8}{5} = 8 \quad \Rightarrow \quad 4x = 8 - \frac{8}{5} = \frac{40}{5} - \frac{8}{5} = \frac{32}{5} \quad \Rightarrow \quad x = \frac{32}{20} = \frac{8}{5}
\]
- Intersection point is \(\left(\frac{8}{5}, \frac{8}{5}\right)\).
---
**Step 4. Summary of Key Points**
- **Line \(4x+y=8\):** Intercepts at \((0,8)\) and \((2,0)\); slope \(-4\).
- **Line \(x+4y=8\):** Intercepts at \((0,2)\) and \((8,0)\); slope \(-\frac{1}{4}\).
- **Line \(x+y=2\):** Intercepts at \((0,2)\) and \((2,0)\); slope \(-1\).
- **Intersection Points:**
- \(x+y=2\) and \(x+4y=8\) intersect at \((0,2)\).
- \(x+y=2\) and \(4x+y=8\) intersect at \((2,0)\).
- \(4x+y=8\) and \(x+4y=8\) intersect at \(\left(\frac{8}{5}, \frac{8}{5}\right)\).
---
**Step 5. Plotting on the Coordinate Plane**
- Draw a coordinate system with appropriate scaling.
- Plot each intercept:
- For \(4x+y=8\): mark \((0,8)\) and \((2,0)\).
- For \(x+4y=8\): mark \((0,2)\) and \((8,0)\).
- For \(x+y=2\): mark \((0,2)\) and \((2,0)\).
- Draw the three straight lines through their respective intercepts.
- Mark the intersection points clearly on the graph.
These steps allow you to accurately graph the three lines and identify their intersections.
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