Hướng dẫn trả lời:
Bài 2:
a) `x^2 + 4x + 4.`
`= x^2 + 2.x.2 + 2^2.`
`= (x + 2)^2.`
b) `x^2 - 8x + 16.`
`= x^2 - 2.x.4 + 4^2.`
`= (x - 4)^2.`
c) `(x + 5).(x - 5).`
`= x^2 - 5^2.`
`= x^2 - 25.`
d) `16x^2 - 8x + 1.`
`= (4x)^2 - 2.4x.1 + 1^2.`
`= (4x - 1)^2.`
e) `(2x - 3)^2 - 25.`
`= (2x - 3)^2 - 5^2.`
`= [(2x - 3) + 5].[(2x - 3) - 5].`
`= (2x - 3 + 5).(2x - 3 - 5).`
`= (2x + 2).(2x - 8).`
f) `(x^2 - x + 1).(x^2 + x - 1).`
`= x^2.(x^2 + x - 1) - x.(x^2 + x - 1) + 1.(x^2 + x - 1).`
`= (x^4 + x^3 - x^2) - (x^3 + x^2 - x) + (x^2 + x - 1).`
`= x^4 + x^3 - x^2 - x^3 - x^2 + x + x^2 + x - 1.`
`= x^4 + (x^3 - x^3) + (- x^2 - x^2 + x^2) + (x + x) - 1.`
`= x^4 - x^2 + 2x - 1.`
