Đáp án+Giải thích các bước giải:
Bài 1:
`a, (2x+1/3y)^2=(2x)^2+2.x.1/3y+(1/3y)^2`
`=4x^2+2/3xy+1/9y^2`
`b, (3x-1/4y)^2=(3x)^2-2.3x.1/4y+(1/4y)^2`
`=9x^2-3/2xy+1/(16y^2`
`c, 9x^2-1/4y^2=(3x)^2-(1/2y)^2`
`=(3x-1/2y).(3x+1/2y)`
Bài 2:
`a, 4x^2+2x+1/4=(2x)^2+2.2x.1/2+(1/2)^2`
`=(2x+1/2)^2`
`b, 25x^2-4xy+4/(25)y^2=(5x)^2-2.5x.2/5+(2/5)^2`
`= (5x - 2/5)^2`
`c, x^2 - 3x + 9/4=x^2-2.x.3/2+(3/2)^2`
`= (x-3/2)^2`
Bài 3:
`a, (3x-y).(3x+y)= (3x)^2-y^2`
` = 9x^2 - y^2`
`b, (1/2x+4y).(1/2x-4y)=(1/2x)^2-(4y)^2 `
`=1/4x^2-16y^2`
`c, 3.(2x-7y).(2x+7y)=3.((2x)^2-(7y)^2)`
`= 3.(4x^2-49y^2)`
