Hướng dẫn trả lời:
Bài 12:
a) `(2x - 3)^2.`
`= (2x)^2 - 2.2x.3 + 3^2.`
`= 4x^2 - 12x + 9.`
b) `(5/2-x)^2.`
`= (5/2)^2 - 2 . 5/2.x + x^2.`
`= 25/4 - 5x + x^2.`
c) `(2x + 3y)^2.`
`= (2x)^2 + 2.2x.3y + (3y)^2.`
`= 4x^2 + 12xy + 9y^2.`
d) `(3x+2/3yz)^2.`
`= (3x)^2 + 2.3x. 2/3yz + (2/3yz)^2`
`= 9x^2 + 4xyz + 4/9y^2z^2.`
e) `({xy}/2 - x/3)({xy}/2 + x/3).`
`= ({xy}/2)^2 - (x/3)^2.`
`= {x^2y^2}/4 - x^2/9.`
Bài 2:
a) `16x^2 + 24x + 9.`
`= (4x)^2 + 2.4x.3 + 3^2.`
`= (4x + 3)^2.`
b) `x^2/4 - 3x + 9.`
`= (x/2)^2 - 2. x/2 . 3 + 3^2.`
`= (x/2 - 3)^2.`
c) `25/x^2 - 10/x + 1.`
`= (5/x)^2 - 2. 5/x. 1 + 1^2.`
`= (5/x - 1)^2.`
d) `4x^4y^8 + (x^2y^4)^4 + 4.`
`= (x^4y^8)^2 + 2.x^4y^8 . 2 + 2^2.`
`= (x^4y^8 + 2)^2.`