Question 542379
{{{ a*b = (1/2)*((a+b)^2 - (a^2 + b^2 ))}}}
{{{ a*b = (1/2)*( a^2 + 2a*b + b^2 - a^2 - b^2 ) }}}
{{{ a*b = (1/2)*( 2a*b ) }}}
{{{ a*b = a*b }}}
OK