To do this, the trinomial must be a perfect square trinomial. This means that the binomial must repeat itself exactly to FOIL out to the trinomial. (5x+ )(5x+ ) The blanks must multiply to equal k and add together to equal 40 when multiplied by 5x. (5x+4)(5x+4) = (5x+4)^2 Applying the FOIL method to the perfect square binomial shows that k=16
