Mathematics
Answer
(x + 4)2 - 5xy - 20y - 6y2 = (x + 4)2 - 5y(x + 4) - 6y2.
Let (x + 4) = t.
(x + 4)2 - 5y(x + 4) - 6y2 = t2 - 5yt - 6y2.
Factorising we get,
t2 - 5yt - 6y2 = t2 - 6yt + 1yt - 6y2.
= t(t - 6y) + y(t - 6y)
= (t - 6y)(t + y)
= (x + 4 - 6y)(x + 4 + y).
Hence, (x + 4)2 - 5xy - 20y - 6y2 = (x + y + 4)(x - 6y + 4).