Derivative of trigonometric function

[tmt1]

A ladder 10 ft long rests against a vertical wall. Let be the
angle between the top of the ladder and the wall and let be
the distance from the bottom of the ladder to the wall. If the
bottom of the ladder slides away from the wall, how fast does
x change with respect to $\theta$ when $\theta \pi/3$?

I'm confused about how to solve this problem.

Let y equal the height of the ladder.

Using the law of sines:

$\frac{10}{sin90} = \frac{x}{sin\frac{\pi}{3}}$

and

$ x= 5\sqrt{3}$

And using the pythagorean theorem:

$y = 5$ when $\theta = \pi/3$

But I'm unsure what to do now.

 

[MarkFL]

You should find:

$$\sin(\theta)=\frac{x}{10}\tag{1}$$

Now, you are asked to find:

$$\left.\d{x}{\theta}\right|_{\theta=\frac{\pi}{3}}\tag{2}$$

So, what should you do to (1) to get a general formula for $$\d{x}{\theta}$$?