Hey there. Studying to retake the SAT. Got a 1400 the first time, shooting for 1550+ this time. Need some help on this question: If n > 0 and 4x^2 + kx + 25 = (2x + n)^2 for all x, what is the value of k + n? The explaination in the book begins with: "We know n is positive and equals 25 when squared..." What I want to know is.. how the heck do they know that? How can you deduce that n = 25 when squared, hence, n = 5? If anyone could explain that to me I'd be very grateful. Thanks.