Hướng dẫn trả lời:
Bài 1:
1) `(x + y)^2.`
`= x^2 + 2xy + y^2.`
2) `(3x+y)^2.`
`= (3x)^2 + 2.3x.y + y^2.`
`= 9x^2 + 6xy + y^2.`
3) `(x^2+2)^2.`
`= x^2 + 2.x.2 +2^2.`
`= x^2 + 4x + 4.`
4) `(2a^2+1/2)^2.`
`= (2a^2)^2 + 2.2a^2 . 1/2 + (1/2)^2.`
`= 4a^4 + 2a^2 + 1/4.`
5) `(4+5/2 e^4)^2.`
`= 4^2 + 2.4. 5/2e^4 + (5/2 e^4)^2.`
`= 16 + 20e^4 + 25/4 e^8.`
Bài 2:
1) `(2x-1)^2.`
`= (2x)^2 - 2.2x.1 + 1^2.`
`= 4x^2 - 4x + 1.`
2) `(x - 1/2)^2.`
`= x^2 - 2.x. 1/2 + (1/2)^2.`
`= x^2 - x + 1/4.`
3) `(y^3 - 3)^2.`
`= (y^3)^2 - 2.y^3 .3 + 3^2.`
`= y^6 - 6y^3 + 9.`
4) `(7 - 2/3b)^2.`
`= 7^2 - 2.7. 2/3b + (2/3b)^2.`
`= 49 - 28/3b + 4/9b^2.`
5) `(6a - 1/3ab)^2`
`= (6a)^2 - 2.6a. 1/3ab + (1/3ab)^2`
`= 36a^2 - 4a^2b + 1/9a^2b^2`
Bài 3:
1) `25x^2 - 4y^2.`
`= (5x)^2 - (2y)^2.`
`= (5x + 2y).(5x - 2y).`
2) `36y^4 - 1/16.`
`= (6y^2)^2 - (1/4)^2.`
`= (6y^2 + 1/4).(6y^2 - 1/4).`