Question 133006
{{{v^3 - 4v^2 - 21v}}}


To begin with, there is at least one 'v' in every term, so factor that out:
{{{v(v^2-4v-21)}}}


Now we know that {{{3*-7=-21}}} and {{{3-7=-4}}}, so:
{{{v^2-4v-21=(v+3)(v-7)}}}


Putting it all together:
{{{v^3 - 4v^2 - 21v=v(v+3)(v-7)}}}