1) Phân tích các đa thức sau thành nhân tử
a) x^2 + 5x + 5xy + 25y
= (x^2 + 5xy) + (5x + 25y)
= x(x + 5y) + 5(x + 5y)
= (x + 5)(x + 5y)
b) x^2 - y^2 + 14x + 49
= (x^2 + 14x + 49) - y^2
= (x + 7)^2 - y^2
= (x - y + 7)(x + y + 7)
c) x^2 - 24x - 25
= (x^2 - 25x) + (x - 25)
= x(x - 25) + (x - 25)
= (x + 1)(x - 25)
d) 4x - 8y = 4(x - 2y)
e) x^2 + 2xy + y^2 - 16
= (x^2 + 2xy + y^2) - 4^2
= (x + y)^2 - 4^2
= (x + y - 4)(x + y + 4)
f) 3x^2 + 5x - 3xy - 5y
= (3x^2 + 5x) - (3xy + 5y)
= x(3x + 5) - y(3x + 5)
= (x - y)(3x + 5)