問題

L.K.

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-

會唔會係0呀
上端移動同下端移動好似冇關係

sosai

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】

畫圖啦.[[tk_28]]

L.K.

畫左都唔識...

piyopiyo

原帖由 L.K. 於 1-7-2008 21:20 發表
畫左都唔識...

x^2+y^2 = 900

differentiate

2x(dx/dy) + 2y = 0
dx/dy = -y/x
-----------------------------
[[tk_32]]

Zend

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

原帖由 Zend 於 1-7-2008 21:47 發表
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...[[tk_36]]

Zend

原帖由 piyopiyo 於 1-7-2008 09:39 PM 發表

x^2+y^2 = 900

differentiate

2x(dx/dy) + 2y = 0
dx/dy = -y/x
-----------------------------
[[tk_32]]

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

原帖由 Zend 於 1-7-2008 21:48 發表

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[[tk_35]]