一條MATH唔識做....

y varies inversely as x^2 = y=k/x^2

IF x increased by 100%,

x y
first 100 100
that 200 Y
when x and y =100 100=k/100^2
k=1000000
so y=1000000/200^2
y=1000000/40000
y=25

2007-09-10 21:45:38 補充：
x yfirst 100 100that 200 Y以上是set了一個圖 當 x是100 y是100時 找出k之後當x是200 y是不明 那by找出k來 找出yso y=25%如有錯 帶望路人來幫手改啦

2007-09-10 21:53:52 補充：
做多小小補充 我上面講 y=25%

2007-09-10 21:54:38 補充：
原本y是100% so y is decrease 75%

2007-09-10 23:47:57 補充：
@O@ decrease 100%?那你可先check數一下..if y decrease 100%... so y will be zero , when y=0, 0=k/x^2so k=0 and x=0 (rej.)so y decrease is impossble 唔知今次得唔得先如果你feel 都係錯 那你試試找你的老師問下吧

2007-09-10 23:50:32 補充：
上面打少左d野- -so y decreased by 100% is impossible when x is increased by 100%

let y = k/x^2
y(new)=k/(2x)^2=(1/4)(k/x^2)
therefore,
the percentage of y decrease
=[k/x^2-(1/4)(k/x^2)] k/x^2*100%
=75%