# 英文算數題解答案

A farmer needs to create a rectangular paddock on land where one long fence already exists. They have 1200m of fencing material to make the other sides of the paddock. What dimensions are required to create the largest possible paddock? What is the area of this paddock(in hectares)? (Hint:Area=Length*Width)

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• 寶寶
Lv 5

A farmer needs to create a rectangular paddock on land where one long fence already exists. They have 1200m of fencing material to make the other sides of the paddock. What dimensions are required to create the largest possible paddock? What is the area of this paddock(in hectares)? (Hint:Area=Length*Width)

他說最長邊已經有了

所以我們把剩下的三邊分別設成X , X , Y

再來我們就可以算他要的Area(綠色部分)了

我們已經知道籬笆總共的長度是1200 m

也就是說 2X + Y = 1200

那我們就可以把Y寫成 Y = (-2X + 1200)

再來我們就來算Area

Area = Length * Width = X * Y = X(-2X + 1200) = -2X2 + 1200X

有了-2X2 + 1200X 我們就能算最大值了

Area = -2 (X2 – 600X) = -2 {(X-300)2 - 90000} = -2(X-300)2 + 180000

所以當X = 300 , Y = 600 時

綠色部分會有最大面積 = 180,000 m2 = 18 hectares

Source(s): me
• PED
Lv 6

SHIUEXP大大,英文不錯

設寬為W , 長邊因為有一邊不用圍 , 長為1200-2W

面積為 W X ( 1200-2W) = 1200W - 2W平方

配方後得到 180000 - 2 (300-W)^2

最大值為寬300 , 長600 , 面積180000平方公尺

Source(s): 數學不錯的我