Đáp án:
`34, 9x^2 + 12x + 4 = (3x)^2 + 2.3x.2 + 2^2 = (3x + 2)^2`
`35, 16x^2 + 8x + 1 = (4x)^2 + 2.4x.1 + 1^2 = (4x + 1)^2`
`36, 4x^2 + 20x + 25 = (2x)^2 + 2.2x.5 + 5^2 = (2x + 5)^2`
`37, 9x^4 + 24x^2 + 16 = (3x^2)^2 + 2 .3x^2 .4 + 4^2 = (2x^2 + 4)^2`
`38, 25x^2 - 20xy + 4y^2 = (5x)^2 - 2.5x.2y + (2y)^2 = (5x - 2y)^2`
`39, 4x^2 - 12xy + 9y^2 = (2x)^2 - 2.2x.3y + (3y)^2 = (2x - 3y)^2`
`40, 25x^2 - 10xy + y^2 = (5x)^2 - 2.5x.y + y^2 = (5x - y)^2`
`41, x^4 - 4x^2 y + 4y^2 = (x^2)^2 - 2.x^2 . 2y + (2y)^2 = (x^2 - 2y)^2`
`42, 9x^2 - 30x + 25 = (3x)^2 - 2.3x.5 + 5^2 = (3x - 5)^2`
`43, 9x^4 - 12x^2 y + 4y^2 = (3x^2)^2 - 2.3x^2 .2y + (2y)^2 = (3x^2 - 2y)^2`
* Áp dụng hằng đẳng thức: `(A + B)^2 = A^2 + 2AB + B^2`
`(A - B)^2 = A^2 - 2AB + B^2`
