By the polynomial remainder theorem, because <em>x</em> = 2<em>i</em> is a zero of <em>f(x)</em>, we have no remainder upon dividing <em>f(x)</em> by <em>x</em> - 2<em>i</em>.
Computing the quotient yields
Then if the remainder term is 0, follows that <em>a</em> = -12.