$$x'' + 3x= 7$$
Given conditions $x'(0)=x'(5)=0$.
I checked the list and I went through three books. I am doing intro to differential equations. I just don't know how to get the extensions... I was told if there is a derivative use $\cos$, but I can't hack it. If there is any simple explanation. Please feel free to expound. This is to simply find the formal solution of the said ODE using Fourier Series. What do I substitute at right hand side? Since I think left hand is simply summation $\cos n \pi/L$.
......I just know that $L=5$? And $7$ is $f(t)$ or $f(x)$? Maybe?