https://s0.wp.com/latex.php?latex=%5Cdisplaystyle+u_C%3D%5Cfrac%7B1%7D%7BRC%7D%5Cint_0%5Et+u-u_C%5C%2C%5Cmathrm%7Bd%7Dt%2Bu_C%280%29&bg=ffffff&fg=1a1a1a&s=0&c=20201002