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Old July 3rd, 2009, 09:06 PM
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Quote:
Originally Posted by calc101 View Post
y = cost kt
y' = -ksinkt
y''= -k^2coskt
4(-k^2coskt) = -25(coskt)

The coskt and the negatives cancel, therefore:
4k^2 = 25
k = \frac{5}{2}

Therefore, the equation is satisfied when k=\frac{5}{2}
I was rather hoping that the OP would make an attempt and say where s/he was stuck if help was still required. Short of using my editing powers, this is now impossible.

As it is, you've left only one trivial (but important) thing for the OP to do. I hope that this one small thing remains left for the OP.
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