V=M\left( a,b,c\right)=\left< a\times b | c\right>\\
M\left( a+b,b+c,c+a\right)=?\\
M\left( a+b,b+c,c+a\right)=\left< \left( a+b\right) \times \left( b+c\right) | c+a \right> =\\
=\left< a\times b + a\times c + b\times b + b \times c|c+a\right> =\\
=\left< a\times b + a\times c + b \times c|c+a\right> =\\
=\left< a \times b| a \right> +\left< a \times b| c \right> +\left< a \times c| a \right> +\left< a \times c| c \right> +\left< b \times c| a \right> +\left< b \times c| c \right> =\\
=0+V+0+0+V+0=2V