Maths Question

5xy(x+y)-25x²y(x+y)²
=5xy(x+y)-5xy(x+y)*5x(x+y) where * -- 乘
=5xy(x+y)[1-5x(x+y)] -------- Select Common factors of two terms
=5xy(x+y)(1-5x² -5xy)
= - 5xy(x+y)(5x² +5xy-1)

5xy(x+y)-25x²y(x+y)²
=5xy(x+y)[1-5x(x+y)]
=5xy(x+y)(1-5x² -5xy)
=-5xy(x+y)(5x² +5xy-1)