https://s0.wp.com/latex.php?latex=%5Cdisplaystyle+G%28x%5E1%2Cx%5E2%2Cx%5E3%29%3D%5Cint%5Climits_%7Bx%5E1%7D%5E%7Bx%5E2%7Df%28t%2Cx%5E3%29%5C%2Cdt&bg=e6e6e6&fg=333333&s=0