SOLUTION: Help! This is one of my homework questions and I did it, but apparently it isn't right?! Given the system of inequalities below, determine the shape of the feasible region and fin

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Question 348482: Help! This is one of my homework questions and I did it, but apparently it isn't right?!
Given the system of inequalities below, determine the shape of the feasible region and find the vertices of the feasible region. Give the shape as "triangle", "quadrilateral", "pentagon", or "unbounded". Report your vertices starting with the one which has the smallest -value. If more than one vertex has the same, smallest -value, start with the one that has the smallest -value. Proceed clockwise from the first vertex. Leave any unnecessary answer spaces blank. Also give the value of the objective function P=-7x-4y for each vertex.
The inequalities are:
x+y>=18
2y-x<=20
5x-y<=53
x>=0
y>=0
and i must give the shape of the area and the coordinates of each vertex

Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Graph each line.
x%2By=18
y=-x%2B18
graph%28300%2C300%2C-2%2C16%2C-2%2C18%2C-x%2B18%29
The region of interest is the shaded region,
Solved by pluggable solver: Plot Any Inequality
Graphing function y%3E=-x%2B18:

graph%28+300%2C+300%2C+-2%2C+16%2C+-2%2C+18%2C+y%3E=-x%2B18+%29


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Find the intersection between the green line and the red line.
%281%2F2%29x%2B10=-x%2B18
x%2B20=-2x%2B36
3x=16
x=16%2F3%7D%7D%0D%0A%7B%7B%7By=-16%2F3%2B54%2F3=38%2F3
(16/3,38/3)
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5x-y=53
y=5x-53
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Find the intersection between the blue line and the red line.
5x-53=-x%2B18
6x=71
x=71%2F6
Then
y=-71%2F6%2B108%2F6=37%2F6
(71/6,37/6)
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Find the intersection between the blue line and the green line.
5x-53=%281%2F2%29x%2B10
10x-106=x%2B20
9x=126
x=14
Then
y=%281%2F2%2914%2B10
y=17
(14,17)
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So the 3 vertices are :
(16/3,38/3)
(71/6,37/6)
(14,17)
Find the value of P=-7x-4y at each vertex.
I will do one, you do the rest.
(14,17):P=-7x-4y=-7%2814%29-4%2817%29=-98-68=-166