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Answer:
[tex]x = \frac{205}{3}[/tex]
[tex]y =\frac{195}{4}[/tex]
Step-by-step explanation:
Given
[tex]p = 410[/tex] --- perimeter
See attachment for fence
Required
x and y
The perimeter of the fence is:
[tex]p = 2(x + y +5 + y) +x[/tex]
Open bracket
[tex]p = 2x + 2y +10 + 2y +x[/tex]
Collect like terms
[tex]p = 2x+x + 2y + 2y+10[/tex]
[tex]p = 3x + 4y+10[/tex]
Substitute: [tex]p = 410[/tex]
[tex]3x + 4y+10 =410[/tex]
Make 4y the subject
[tex]4y =410-10-3x[/tex]
[tex]4y =400-3x[/tex]
Make y the subject
[tex]y =\frac{400-3x}{4}[/tex]
The area (A) of the fence is:
[tex]A = (y + y + 5) * x[/tex]
[tex]A = (2y + 5) * x[/tex]
Substitute: [tex]y =\frac{400-3x}{4}[/tex]
[tex]A = (2*\frac{400-3x}{4} + 5) * x[/tex]
[tex]A = (\frac{400-3x}{2} + 5) * x[/tex]
Take LCM
[tex]A = (\frac{400-3x+10}{2}) * x[/tex]
Solve like terms
[tex]A = (\frac{410-3x}{2}) * x[/tex]
Open bracket
[tex]A = \frac{410x-3x^2}{2}[/tex]
Remove fraction
[tex]A = 205x-1.5x^2[/tex]
Differentiate both sides
[tex]A' = 205 - 3x[/tex]
To maximize; set [tex]A' =0[/tex]
[tex]205 - 3x =0[/tex]
Solve for 3x
[tex]3x = 205[/tex]
Solve for x
[tex]x = \frac{205}{3}[/tex]
Recall that: [tex]y =\frac{400-3x}{4}[/tex]
So, we have:
[tex]y =\frac{400-3*205/3}{4}[/tex]
[tex]y =\frac{400-205}{4}[/tex]
[tex]y =\frac{195}{4}[/tex]
