Đáp án:
Giải thích các bước giải:
`a)(2x+3y)^2`
`=(2x)^2 + 2.2x.3y + (3y)^2`
`=4x^2 + 12xy +9y^2`
`b)(5x-y)^2`
`=(5x)^2 -2.5x.y +y^2`
`=25x^2 -10xy +y^2`
`c)(2x - 5/2 y)^2`
`=(2x)^2 -2.2x. 5/2 y + (5/2 y)^2`
`=4x^2 -10xy + 25/4 y^2`
`d) (x^2 + 2/5 y) (x^2 -2/5 y)`
`=(x^2)^2 - (2/5 y)^2`
`=x^4 - 4/25 y^2`
`e)(x+ 1/4)^2`
`=x^2 +2.x.1/4 + (1/4)^2`
`=x^2 +1/2 + 1/16`
`f) (2/3 x +1/3 y)^2`
`=(2/3 x)^2 + 2.2/3 x .1/3 y + (1/3 y)^2`
`=4/9 x^2 + 4/9 xy + 1/9 y^2`
