Question 133796
This is the difference of two squares, the pattern is {{{a^2-b^2=(a+b)(a-b)}}}.  Just substitute {{{a=(c+d)}}} and {{{b=(c-d)}}}


{{{((c+d)+(c-d))((c+d)-(c-d))}}}
{{{(2c)(2d)}}}
{{{4cd}}}