Thread: laplace sum

solve x''+9x=cos3t where x(0)=1 and x(pi/2)=-1

here x'(0) is not given and i am unable to use x(pi/2)=-1

please help!!

You don't need to use Laplace Transforms at all, simply solve the homogeneous equation and then apply the method of undetermined coefficients...

Originally Posted by prasum

solve x''+9x=cos3t where x(0)=1 and x(pi/2)=-1

here x'(0) is not given and i am unable to use x(pi/2)=-1

please help!!

Hi prasum!

If you want you can still solve it with Laplace.
Just consider x'(0) an unknown constant for now and solve the differential equation.
Then, after you get your solution for x(t), fill in t=pi/2 and deduce what x'(0) must be.

thanks