Use V 2 ( x ) = 1 2 x 1 2 + 1 2 ( x 2 + b c − a x 1 ) 2 {\displaystyle V_{2}(x)={\frac {1}{2}}x_{1}^{2}+{\frac {1}{2}}(x_{2}+{\frac {b}{c-a}}x_{1})^{2}\,} (change the " − {\displaystyle -\,} " to " + {\displaystyle +\,} ").
--Shuo
(change the "
" to "
").
