# Problem about a robotic arm

1. Mar 25, 2013

### supermiedos

1. The problem statement, all variables and given/known data

Given the following robotic arm:
http://i.imgur.com/TIb1vOk.png

and knowing that $x_{c}$ = Lcosθ and $y_{c}$ = Lsinθ, find expressions for
$x_{m}$ and $y_{m}$ and show that:
d$x_{m}$ = -$y_{m}$dθ + ($y_{c}$-$y_{m}$)d$\phi$

2. Relevant equations

(Shown on picture below)

3. The attempt at a solution
Here it is my attempt at a solution:
http://i.imgur.com/Ee7iZWk.png

First I made a traslation to the origin and then I found the angles. Then, I got that triangle (4th pic) and found the relations between the angles and the sides. Next, I simplified both expressions using trigonometric identities and finally got d$x_{m}$.

But I don't get the book's answer!!! Could you help me please?