# Expression for motion

1. Jan 6, 2006

### Reshma

I need your guidance in this problem.

Problem:
The midpoint of a stretched string of length 'L' is pulled a distance U = L/10 from its equilibrium position so that the string forms 2 sides of an isosceles triangle. The string is then released. Find the expression for the motion by the Fourier series method.

My problem is I have no idea of how Fourier analysis is done cause my course never included this topic. But the formula hinted in my text is:
$$U(x,t) = \sum_n\left[A_n\sin \frac{n\pi x}{L}\cos \frac{n\pi ct}{L} + B_n\sin \frac{n\pi x}{L}\sin \frac{n\pi ct}{L}\right]$$
Can someone help me out here?

2. Jan 10, 2006

### Reshma

Never mind, I found the solution !