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Find the maximum value of 4x+y if:

 

3x+y  ≤ 31

 

2x+y  ≤ 23

 

2x-y  ≤ 14

 

x+6y  ≥ 20

 

y ≤ 11

 

y ≥ 0

 

x ≥ 2

 Dec 20, 2016

Best Answer 

 #1
avatar+129852 
+5

The max will occur at a "corner point" but this is very hard to identify with a graph because there are so many "overlapping"  graphs....

 

WolframAlpha gives the following solution : 

 

https://www.wolframalpha.com/input/?i=maximize+4x+%2By+given+3x%2By++%E2%89%A4+31+,++2x%2By++%E2%89%A4+23,+++2x-y++%E2%89%A4+14,+++x%2B6y++%E2%89%A5+20,+++y+%E2%89%A4+11,+++y+%E2%89%A5+0,+++x+%E2%89%A5+2

 

It appears that the max occurs at (9, 4)   and the max is  4(9)  + 4   = 40

 

Here's the Desmos graph : https://www.desmos.com/calculator/opl1cuchfu

 

Maybe you can find the max corner point much easier than I can.......!!!!!

 

 

cool cool cool

 Dec 20, 2016
 #1
avatar+129852 
+5
Best Answer

The max will occur at a "corner point" but this is very hard to identify with a graph because there are so many "overlapping"  graphs....

 

WolframAlpha gives the following solution : 

 

https://www.wolframalpha.com/input/?i=maximize+4x+%2By+given+3x%2By++%E2%89%A4+31+,++2x%2By++%E2%89%A4+23,+++2x-y++%E2%89%A4+14,+++x%2B6y++%E2%89%A5+20,+++y+%E2%89%A4+11,+++y+%E2%89%A5+0,+++x+%E2%89%A5+2

 

It appears that the max occurs at (9, 4)   and the max is  4(9)  + 4   = 40

 

Here's the Desmos graph : https://www.desmos.com/calculator/opl1cuchfu

 

Maybe you can find the max corner point much easier than I can.......!!!!!

 

 

cool cool cool

CPhill Dec 20, 2016
 #2
avatar+129852 
+5

Let's look at this again......and we will remove the last 3 constraints.....these three just tell us that  the solution will occur in the first quadrant  where x  ≥ 2  and   y ≤ 11

 

Look at the graph now : https://www.desmos.com/calculator/upxf7i7tbd

 

If I read the graph correctly.....[a real leap of faith]...there appear to be only two corner points that satisfy the constraints....they are

 

(8,2)   and (9,4).......but only one will maximize  4x + y....and that occurs at (9,4)

 

 

cool cool cool

 Dec 20, 2016

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