Asked by sal
                You are making a rectangle from two horizontal rods and two vertical rods. Horizontal rods cost $3 per foot and vertical rods cost $5 per foot. If your budget is $180, then what area is the largest possible area of the rectangle?
Not sure how to start it off..please help
            
        Not sure how to start it off..please help
Answers
                    Answered by
            Reiny
            
    let the length of the horizontal be x ft
let the length of the vertical be y ft
restraint: 3x + 5y =180
y = (180 - 3x)/5 = 36 -(3/5)x
area = xy = x(36 - (3/5)x) = 36x - (3/5)x^2
d(area)/dx = 36 - (6/5)x
= 0 for a max area
(6/5)x = 36
take over ....
    
let the length of the vertical be y ft
restraint: 3x + 5y =180
y = (180 - 3x)/5 = 36 -(3/5)x
area = xy = x(36 - (3/5)x) = 36x - (3/5)x^2
d(area)/dx = 36 - (6/5)x
= 0 for a max area
(6/5)x = 36
take over ....
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