https://s0.wp.com/latex.php?latex=S+%3D+%5Cfrac%7B1%7D%7B2%7D+%28a%2Bb%2Bc%29+%3D+%5Cfrac%7B1%7D%7B2%7D+%2850%2B48%2B14%29+%3D+56+&bg=%23ffffff&fg=%23111111&s=0