Optimize Derivative of Trig Functions Grade 11 Math

[livelaughlove]

Homework Statement

there's a picture of the question... from my textbook
http://photos-h.ak.fbcdn.net/hphotos..._1385551_n.jpg
thers a diagram image of the problem too to help understand

Homework Equations

well its a word problem,
i used cosine rule at beginining and then pythagoras...i don't know what to do next but i think you calculare the area and then derivative. but i don't know how (whats the equation for the area)

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 !

 

[Altabeh]

Homework Statement

there's a picture of the question... from my textbook
http://photos-h.ak.fbcdn.net/hphotos..._1385551_n.jpg
thers a diagram image of the problem too to help understand

Homework Equations

well its a word problem,
i used cosine rule at beginining and then pythagoras...i don't know what to do next but i think you calculare the area and then derivative. but i don't know how (whats the equation for the area)

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 !

I can't get access to that web site... so you better go with another uploading site like tinypic.com or somewhere else!

AB

 

[livelaughlove]

oh sorry ! here you go
i hope this way works

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

and here's the old link again, fixed it

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

 

[Altabeh]

oh sorry ! here you go
i hope this way works

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

and here's the old link again, fixed it

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

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

http://www.freeimagehosting.net/uploads/th.3b37fcda70.jpg

As for the second question, the only hint is that take the first derivative of the area with respect to theta and then equate the resulting equation with zero. The theta from the new equation with an accuracy of 1/10 of a degree will be your desirable answer.

AB