Question 22744
Notice that the first term (16y^2) and the last term (25x^2) are perfect squares, this suggests that the factors may be identical, so try: 
{{{(4y + 5x)(4y + 5x)}}} Use the FOIL method to check it out.

{{{(4y + 5x)(4y + 5x) = 16y^2 + 20xy + 20xy + 25x^2}}} = {{{16y^2 + 40xy + 25x^2}}}