1. The problem statement, all variables and given/known data http://u1.imgupload.co.uk/1257811200/9e4e_image.bmp 2. Relevant equations find above 3. The attempt at a solution in fact i had no problem in the progress of doing this question and finally i got F(s)= 1/1+s^2 and i want to ask it is vaild for all value of s since it is s^2? is it true for no matter s is >0 or s is <0?