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等我黎幫你啦~其實呢.你係唔係讀緊英中呀...如果係既..其實有d字你唔識都唔係好緊要..由其係數學...見得多..見到有呢隻字既..你都會知道佢想你用咩方法做..習慣下就得嫁啦...我都係咁~

****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._."

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!!!