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where is the light initially?
20 meters from the flagpole! coming from the top
dL/dt = 5 ....dh/dt = 0 dx/dt =? dx/dt = dx/dL * dx/dt find dx/dL ?? maybe not tho.....
is there an initial height of the light?
ahhh...... the shadow moving problem in all the textbooks :)
well you need to cross multiply and divide. so it would be 20m/50m by 5m/x.... that would be 50x by 100... divide 50 by 100 to get x alone and you get x=2
thats a rough drawing by the way :)
h/(20+x) = 10/(x) if that helps :)
lol sorry thats what was given to me :p
y = (200+10x)/x
dx/dt = x^2(dy/dt)/-200 ?? maybe
dy/dy = 5
im gonna take a gander and say... 25(5) = 125 125/-200 = ?? -.0625 ?? if I did it right lol
i think I got the "equation" wrong at the start....
lol thank you! ..but i dont understand how can you have dy/dy? :s
lol so the whole thing is wrong??
:) fat fingers...little tiny keyboard :)
LMAO! ohhhh i see (:
it may be right, but I dont trust it yet.... need to find the equation to derive; then the rest is easy.
ya but thats the part i cant get! wahh :(
I am thinking it is the relation of congruent triangles; "y" being the height of the lamp: x = length of shadow. 10/x = y/(20+x) is what I come up with; there is no question about the distance of the light to the tip of the shadow...
10(20+x) = y(x) (200+10x)/x = y 200/x + 10 = y 200/x = y-10 200/(y-10) = x ??? sounds good
this relate y and x..... now implicit it with respect to time right?
yea thats what i gotta do
and thank youuu! for everything so far btw!
-200(dy/dt) / (y-10)^2 = dx/dt dy/dt = 5 y = 50;
no prob; I live to math things up lol
-0.625 is what i get, and I am almost sure its right... but i get that nagging feeling that I am just being stupid :)
hahaha but where did u get negative two hundred?
ok.... step it out.... 200 x = ------- (y-10) (y-10)(0) - (200)(dy/dt) dx/dt = ---------------------- (y-10)^2
lol im on the phone with my friend trying to figure this out and im reading her what u wrote and we both agreed your funny, just thought id let you know :p but yea we dont understand also where you got the 50 from? (: care to explain?
-200(dy/dt) dx/dt = ------------- (y-10)^2
when y=50...its right there :)
dy/dt is given already as the rate of change in "y"... = 5 m/s
as y rises; x shrinks.... so its (-) direction..
ohhh okay! thank you so so much honestly, it means a lot (: (:
just let me know if im right :)
i will haha but its the first time im on this site so how can i tell you?
because i have to check with my teacher first
shout really loud? :) AMISTRE WAS RIGHT!!!.... or if im wrong it would be: AMISTRE WAS WRONG .... ill feel it either way :)
that moving shadow thing is in all the calc textbooks If seen, and it always makes me nervous
lol im sure you got it right though, it seemed to make sense. i found it impossible!
good luck :)
thank you again!:)