Linear Programming C92Fa5
1. **State the problem:**
Maximize the objective function $$P = 8x + 6y$$
subject to the constraints:
$$x + 4y \geq 8$$
$$3x + 6y \geq 12$$
$$2x + y \leq 6$$
$$x \geq 0$$
$$y \geq 0$$
2. **Identify the feasible region:**
The feasible region is the set of points $(x,y)$ that satisfy all constraints simultaneously.
3. **Find the intersection points (vertices) of the feasible region:**
- From $$x + 4y = 8$$, when $x=0$, $y=2$; when $y=0$, $x=8$.
- From $$3x + 6y = 12$$, when $x=0$, $y=2$; when $y=0$, $x=4$.
- From $$2x + y = 6$$, when $x=0$, $y=6$; when $y=0$, $x=3$.
4. **Calculate vertices by solving pairs of equations:**
- Intersection of $$x + 4y = 8$$ and $$2x + y = 6$$:
Multiply first equation by 2:
$$2x + 8y = 16$$
Subtract second equation:
$$(2x + 8y) - (2x + y) = 16 - 6$$
$$7y = 10$$
$$y = \frac{10}{7} \approx 1.43$$
Substitute back:
$$x + 4 \times \frac{10}{7} = 8$$
$$x = 8 - \frac{40}{7} = \frac{56}{7} - \frac{40}{7} = \frac{16}{7} \approx 2.29$$
Vertex: $\left(\frac{16}{7}, \frac{10}{7}\right)$
- Intersection of $$3x + 6y = 12$$ and $$2x + y = 6$$:
From second equation:
$$y = 6 - 2x$$
Substitute into first:
$$3x + 6(6 - 2x) = 12$$
$$3x + 36 - 12x = 12$$
$$-9x = -24$$
$$x = \frac{24}{9} = \frac{8}{3} \approx 2.67$$
Then:
$$y = 6 - 2 \times \frac{8}{3} = 6 - \frac{16}{3} = \frac{18}{3} - \frac{16}{3} = \frac{2}{3} \approx 0.67$$
Vertex: $\left(\frac{8}{3}, \frac{2}{3}\right)$
- Intersection of $$x + 4y = 8$$ and $$3x + 6y = 12$$:
Multiply first equation by 3:
$$3x + 12y = 24$$
Subtract second equation:
$$(3x + 12y) - (3x + 6y) = 24 - 12$$
$$6y = 12$$
$$y = 2$$
Substitute back:
$$x + 4 \times 2 = 8$$
$$x = 8 - 8 = 0$$
Vertex: $(0, 2)$
5. **Evaluate the objective function at each vertex:**
- At $(0, 2)$:
$$P = 8(0) + 6(2) = 12$$
- At $\left(\frac{16}{7}, \frac{10}{7}\right)$:
$$P = 8 \times \frac{16}{7} + 6 \times \frac{10}{7} = \frac{128}{7} + \frac{60}{7} = \frac{188}{7} \approx 26.86$$
- At $\left(\frac{8}{3}, \frac{2}{3}\right)$:
$$P = 8 \times \frac{8}{3} + 6 \times \frac{2}{3} = \frac{64}{3} + \frac{12}{3} = \frac{76}{3} \approx 25.33$$
- At $(0,6)$ (from $2x + y \leq 6$ when $x=0$):
$$P = 8(0) + 6(6) = 36$$
6. **Check feasibility of $(0,6)$:**
- $x + 4y = 0 + 24 = 24 \geq 8$ ✓
- $3x + 6y = 0 + 36 = 36 \geq 12$ ✓
- $2x + y = 0 + 6 = 6 \leq 6$ ✓
- $x \geq 0$, $y \geq 0$ ✓
7. **Conclusion:**
The maximum value of $P$ is 36 at the vertex $(0,6)$.
**Final answer:**
$$\boxed{\max P = 36 \text{ at } (0,6)}$$