L.K. 發表於 30-6-2008 04:05:09

問題

1.)一塊長30cm ge木倚在牆邊,當佢ge上端下降了6cm時,佢ge下端移左幾多?

-終場ソ使者- 發表於 30-6-2008 13:50:44

會唔會係0呀
上端移動同下端移動好似冇關係

sosai 發表於 30-6-2008 20:31:19

回復 2# 的帖子

唔會
佢FIX左塊木係30CM
好似響中三SIN COS果課見過
應該唔係用PYTH.THM做

[S]【YU】 發表於 1-7-2008 10:05:53

畫圖啦.[]

L.K. 發表於 1-7-2008 21:20:59

畫左都唔識...

piyopiyo 發表於 1-7-2008 21:39:33

原帖由 L.K. 於 1-7-2008 21:20 發表 http://www.nakuz.com/bbs/images/common/back.gif
畫左都唔識...
x^2+y^2 = 900

differentiate

2x(dx/dy) + 2y = 0
dx/dy = -y/x
-----------------------------
[]

Zend 發表於 1-7-2008 21:47:37

正常少少ge maths

let x,y
x^2+y^2= 900
now
(x-k)^2 + (y+6)^2=900

x^2+y^2 = (x-k)^2+(y+6)^2
x^2+y^2 = x^2-2kx+k^2+y^2+12y+36
-2kx+k^2+12y+36=0

k^2-2xk +(12y+36) =0
find k =.="
佢的值受initial value 影響ga bor

piyopiyo 發表於 1-7-2008 21:48:32

原帖由 Zend 於 1-7-2008 21:47 發表 http://www.nakuz.com/bbs/images/common/back.gif
正常少少ge maths

let x,y
x^2+y^2= 900
now
(x-k)^2 + (y+6)^2=900

x^2+y^2 = (x-k)^2+(y+6)^2
x^2+y^2 = x^2-2kx+k^2+y^2+12y+36
-2kx+k^2+12y+36=0

k^2-2xk +(12y+36) =0
find k =.="
佢的值受 ...
我ge結論同Zend叔一樣...[]

Zend 發表於 1-7-2008 21:48:48

原帖由 piyopiyo 於 1-7-2008 09:39 PM 發表 http://www.nakuz.com/bbs/images/common/back.gif

x^2+y^2 = 900

differentiate

2x(dx/dy) + 2y = 0
dx/dy = -y/x
-----------------------------
[]
你唔係with respect to t =.=
另外y變,x變
要用partial differentiation 先得
而資料都好似唔夠

piyopiyo 發表於 1-7-2008 21:53:18

原帖由 Zend 於 1-7-2008 21:48 發表 http://www.nakuz.com/bbs/images/common/back.gif

你唔係with respect to t =.=
另外y變,x變
要用partial differentiation 先得
而資料都好似唔夠
原來我錯左[]
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