lost all my notes from the class. doh.

ax''+cx=0

assume both a and c are >0

i get:

x(t)=C1cos(sqrt(ac)/a*t)+C2sin(sqrt(ac)/a*t)

this seem right?

8/27/2008 4:54:54 PM

wrong

8/27/2008 5:06:40 PM

well what'd you get?

8/27/2008 5:15:02 PM

your characteristic equation will be:

a*r^2 + c = 0

assuming a and c are positive, your roots are:

[0 +/- sqrt(-4ac)]/2a which simplifies to

0 +/- (sqrt(ac)/a)i

so you will have imaginary roots. Alpha = 0 and Beta = sqrt(ac)/a

you'll end up with x(t) = C1*cos[(sqrt(ac)/a)*t]+C2*sin[(sqrt(ac)/a)*t]

which is pretty much what you had, but your t was in the denominator (or you were missing some parentheses)

[Edited on August 27, 2008 at 6:15 PM. Reason : ]

8/27/2008 6:11:48 PM

well, on my notebook paper it's not in the denominator

tww needs an equation editor

thanks so much TenaciousC! i guess i just wanted some reassurance

8/27/2008 6:21:14 PM