1. 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

2. Re: laplace sum

If you have to use Laplace Transforms, (there are other methods available), run the calculation through with x'(0) as an unknown constant. When you have your solution for x, substitute t=pi/2, x=-1 to evaluate the constant.