# HELP optimization derivative of trig functions, grade 11 math,give it a try please !

1. Jan 9, 2010

### livelaughlove

1. The problem statement, all variables and given/known data
there's a picture of the question... from my text book
http://photos-h.ak.fbcdn.net/hphotos..._1385551_n.jpg [Broken]
thers a diagram image of the problem too to help understand

2. Relevant equations

well its a word problem,
i used cosine rule at beginining and then pythagoras...i dont know what to do next but i think you calculare the area and then derivative. but i dont know how (whats the equation for the area)

3. The attempt at a solution
well i used the cosine rule for triangle BCO
BC^2 = 10^2 + 10^2 - 2x10x10 cosθ
BC = √(200-200cosθ)
XY = BC

BY^2 = BX^2 + XY^2 =
400 = BX^2 + (200-200cosθ)
BX^2 = 200 + 200cosθ
BX = √(200+200cosθ)

now what do i do?

reply asap ! :P thankss !!

Last edited by a moderator: May 4, 2017
2. Jan 9, 2010

### Altabeh

Re: HELP optimization derivative of trig functions, grade 11 math,give it a try pleas

AB

Last edited by a moderator: May 4, 2017
3. Jan 9, 2010

### livelaughlove

Re: HELP optimization derivative of trig functions, grade 11 math,give it a try pleas

oh sorry ! here you go
i hope this way works

http://es.tinypic.com/r/2exa4yb/6

and heres the old link again, fixed it

http://photos-h.ak.fbcdn.net/hphotos-ak-snc3/hs145.snc3/17245_418921415214_614755214_10740817_1385551_n.jpg [Broken]

Last edited by a moderator: May 4, 2017
4. Jan 9, 2010

### Altabeh

Re: HELP optimization derivative of trig functions, grade 11 math,give it a try pleas

I've given all hints needed for the complete answer in the following picture: