Respuesta :
A rectangle, let length=a and width=b
perimeter: a+a+b+b=820
2a+2b=820 --> a+b = 410
Make a or b the subject: a=410-b
Area: ab=42 000 (area of a rectangle, length x width)
Sub a in.
b(410-b) = 42000
Expand: 410b - b^2 = 42000
Rearrange and use quadratic formula: b^2 -410b + 42000=0
b= 210 (can only be positive because length cannot be negative)
Sub this value back into perimeter or area equation: a + 210 = 410 --> a =200
Therefore, a= 200 and b=210.
Depending what you made the width is, it should be 200ft.
(I may have made some calculation errors as i'm not used to typing it out, but the process should be correct) I hope helps! :)
