Answer
$5(5x+y)^2$
Work Step by Step
The product of a binomial sum and a binomial difference is: $(A+B)(A-B)=A^2-B^2$.
The square of a binomial sum is: $(A+B)^2=A^2+2AB+B^2$.
The square of a binomial difference is: $(A-B)^2=A^2-2AB+B^2$.
Hence here: $125x^2+50xy+5y^2=\\=5(25x^2+10xy+y^2)\\=5((5x)^2+2\cdot5x\cdot y+(y)^2)\\=5(5x+y)^2$
