Step-by-step explanation:
Here (1)(25) = 25 and its factor pairs are 1 & 25, and 5 & 5. 5 + 5 = 10, so we can rewrite the xy term as 10xy = 5xy + 5xy.
y2 + 10xy + 25x2 = y2 + (5xy + 5xy) + 25x2
= (y2 + 5xy) + (5xy + 25x2) = y(y + 5x) + 5x(y + 5x)
= (y + 5x)(y + 5x) = (y + 5x)2
