Find solution using graphical method
MAX z = 15x1 + 10x2
subject to
4x1 + 6x2 <= 360
3x1 <= 180
5x2 <= 200
and x1,x2 >= 0 Solution:Problem is | MAX `z` | `=` | `` | `15` | `x_1` | ` + ` | `10` | `x_2` |
|
| subject to |
| `` | `4` | `x_1` | ` + ` | `6` | `x_2` | ≤ | `360` | | `` | `3` | `x_1` | | | | ≤ | `180` | | | | `` | `5` | `x_2` | ≤ | `200` |
|
| and `x_1,x_2 >= 0; ` |
Hint to draw constraints
1. To draw constraint `color{red}{4x_1+6x_2<=360} ->(1)`
Treat it as `color{red}{4x_1+6x_2=360}`
When `x_1=0` then `x_2=?`
`=>4(0)+6x_2=360`
`=>6x_2=360`
`=>x_2=(360)/(6)=60`
When `x_2=0` then `x_1=?`
`=>4x_1+6(0)=360`
`=>4x_1=360`
`=>x_1=(360)/(4)=90`
Put `x_1=0,x_2=0` (origin) in `color{red}{4x_1+6x_2<=360}`, then `0+0<=360`, which is true,
The half plane containing the origin is the region of the solution set of the inequation `color{red}{4x_1+6x_2<=360}`
2. To draw constraint `color{green}{3x_1<=180} ->(2)`
Treat it as `color{green}{3x_1=180}`
`=>x_1=(180)/(3)=60`
Here line is parallel to Y-axis
Put `x_1=0,x_2=0` (origin) in `color{green}{3x_1<=180}`, then `0<=180`, which is true,
The half plane containing the origin is the region of the solution set of the inequation `color{green}{3x_1<=180}`
3. To draw constraint `color{blue}{5x_2<=200} ->(3)`
Treat it as `color{blue}{5x_2=200}`
`=>x_2=(200)/(5)=40`
Here line is parallel to X-axis
Put `x_1=0,x_2=0` (origin) in `color{blue}{5x_2<=200}`, then `0<=200`, which is true,
The half plane containing the origin is the region of the solution set of the inequation `color{blue}{5x_2<=200}`

The value of the objective function at each of these extreme points is as follows:
Extreme Point Coordinates (`x_1`,`x_2`) | Lines through Extreme Point | Objective function value `z=15x_1 + 10x_2` |
| `color{red}{O(0,0)}` | `color{black}{4->x_1>=0}` `color{black}{5->x_2>=0}` | `15(0)+10(0)=0` |
| `color{green}{A(60,0)}` | `color{green}{2->3x_1<=180}` `color{black}{5->x_2>=0}` | `15(60)+10(0)=900` |
| `color{blue}{B(60,20)}` | `color{red}{1->4x_1+6x_2<=360}` `color{green}{2->3x_1<=180}` | `15(60)+10(20)=1100` |
| `color{brown}{C(30,40)}` | `color{red}{1->4x_1+6x_2<=360}` `color{blue}{3->5x_2<=200}` | `15(30)+10(40)=850` |
| `color{darkorange}{D(0,40)}` | `color{blue}{3->5x_2<=200}` `color{black}{4->x_1>=0}` | `15(0)+10(40)=400` |
The maximum value of the objective function `z=1100` occurs at the extreme point `(60,20)`.
Hence, the optimal solution to the given LP problem is : `x_1=60, x_2=20` and max `z=1100`.
This material is intended as a summary. Use your textbook for detail explanation.
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