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# maths <

****please using the completing the square****

我仲想要埋解釋，因為我唔知點做啊！！ｔｈｘ～～

In the following function , find the maximum or minimum value and write down the axis of symmetry of the graph.

(a) f(x)=4x+6-x^2

2(a)The cost of producing a computer by a company is given by $C , and

C=5x^2-500x+1500 where x is the number of computer produced daily.

(a)Find x so that the cost is minimum

(b)Find that minimum cost

### 2 Answers

- 1 decade agoFavorite Answer
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****please using the completing the square****

請用配方(completing the square)

In the following function , find the maximum or minimum value and write down the axis of symmetry of the graph.

根據以下方程式, 找出最高或最低的數值及圖中畫出對稱的)軸線

(a) f(x)=4x+6-x^2 *先排番好次序 a^2+bx+c

x^2+4x+6=f(x) *再做 completing the square = 抽b(姐係式入面既4

[x^2+4x+(4/2)^2]-(4/2)^2+6 *+(b/2)^2-b/2)^2 有+就一定有-

(x+4)^2+10 *最後整係要+果個..-果個拿出黎俾c去+or-

*咁c既數字就係係圖入面最高or最低既一點

*要睇佢係maximum or minimum 就睇個數本身a係正定副

*正既就係 minimum 刓就係maximum

2(a)The cost of producing a computer by a company is given by $C , and C=5x^2-500x+1500 where x is the number of computer produced daily.

2(a)一部電腦製造出來的價錢是$C, 和C=5x^2-500x+1500 而x是每日電腦會製造出來的數量

(a)Find x so that the cost is minimum

(b)Find that minimum cost

a. 搵出x 而係最少數量

b. 搵出最少數量既數值..

5x^2-500x+1500 抽個5出黎

5(x^2-100x+300) 之後做completing square roots

5((x^2-100x+(100/2)^2)-(100/2)^2+300)

抽番(100/2)^2+300出黎..記得*番5

5(x-50)^2-11000

a. x=50 要把5(x-50)呢個數..x要幾多先會=0...所以x要=50先會50-50=0

b. minimum cost : 11000

如果冇意外我訐錯既話..就應該係咁計-_-"希望你明我講我乜啦._."

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- 1 decade ago
a>

f(x)=4x+6-x^2

>>f(x)=-x^2+4x+6

>>f(x)=-(x^2-4x+4-4)+6

>>f(x)=-(x^2-4x+4)+4+6 (用completing the square method,即係令到你可以整到個square,,令變走咗個4x咁煩)

>>f(x)=-(x-2)^2+10

therefore the maximum value is 10, when x=2 <<(因為佢前面係負數..所以係有maximum)

幅圖你自己畫,記住好似一條橋咁

咁你可insert幾個points..分別為:

vertex:(2,10),

y-intercept:(0,6)

x-intercept:(2+√10,0);(2-√10,0)

cause...when y=0,即

f(x)=0

then -(x-2)^2+10 =0

>>>>>(x-2)^2 =10

>>>>>x-2=+/-√10

>>>>>x=2+/-√10

2008-11-03 20:17:48 補充：

mdkhs914 佢都無point出the axis of symmetry.!!!

同埋佢答第二條個陣仲存在問題...!!!所以唔完整!!!

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