https://s0.wp.com/latex.php?latex=%5Cdisplaystyle+%5Cfrac%7B%5Clangle+v%2Cv%5Crangle+%5Clangle+x%2Cx+%5Crangle+-+%5Clangle+v%2Cx+%5Crangle%5E2%7D%7B%5Clangle+x%2Cx+%5Crangle%7D+%5Cgeq+0&bg=ffffff&fg=333333&s=0&c=20201002