## Intermediate Algebra (6th Edition)

$(5x+4)^2$
The two numbers whose product is $25(16)=40$ and whose sum is $40$ are $\{ 20,20 \}$. Using these numbers to decompose the middle term of the trinomial results to \begin{array}{l} 25x^2+40x+16 \\= 25x^2+20x+20x+16 \\= (25x^2+20x)+(20x+16) \\= 5x(5x+4)+4(5x+4) \\= (5x+4)(5x+4) \\= (5x+4)^2 .\end{array}