# Differential equations

1. Mar 18, 2008

### supermesh

We have these two equations:
dx/dt = -k1 (y)
dy/dt = k2 x
k1= 10 k2= 10
These are the conditions:
x(0)= 100
y(0) = 0

I am so confused.....This is what I have done so far....but is not making any sense...

x= (dy/dt) (1/k2)
Substitute in:

d2y/dt2 = -100 y

So the solution is

Y= c1 cos 10x+ c2 sin 10x

I don't know how to use boundary counditions now....Is this even a right approach?

Thank you so much

2. Mar 18, 2008

### Snazzy

The rule for a differential equation:
$$\frac{dy}{dt}=ky$$
$$y(t)=y_0e^k^t$$

3. Mar 18, 2008

### D H

Staff Emeritus
Good so far.

There is no x in your differential equation; why do you have one here? Try finding the solution to the second order differential equation again.