Đáp án+Giải thích các bước giải:
Bài 1:
`a)(2x+1/3y)²=(2x)²+2.2x. 1/3y+(1/3y)²=4x²+4/3xy+1/9y²`
`b)(3x-1/4y)²=(3x)²-2.3x. 1/4y+(1/4y)²=9x²-3/2xy+1/16y²`
`c)9x²-1/4y²=(3x)²-(1/2y)²=(3x+1/2y)(3x-1/2y)`
Bài 2:
`a)4x²+2x+1/4=(2x)²+2.2x. 1/2+(1/2)²=(2x+1/2)²`
`b)25x²-4xy+4/25y²=(5x)²-2.5x. 2/5y+(2/5y)²=(5x-2/5y)²`
`c)x²-3x+9/4=x²-2.x. 3/2+(3/2)²=(x-3/2)²`
Bài 3:
`a)(3x-y).(3x+y)=(3x)²-y²=9x²-y²`
`b)(1/2x+4y).(1/2x-4y)=(1/2x)²-(4y)²=1/4x²-16y²`
`c)3.(2x-7y).(2x+7y)=3.[(2x)²-(7y)²]=3.(4x²-49y²)=12x²-147y²`
Bài 4:
`a)(x+3)²-(x-2)(x+4)-4x`
`=x²+6x+9-(x²+4x-2x-8)-4x`
`=x²+6x+9-x²-4x+2x+8-4x`
`=17`
`b)(2x+5)(2x-5)-(2x-3)²-12x`
`=(4x²-25)-(4x²-12x+9)-12x`
`=4x²-25-4x²+12x-9-12x`
`=-34`
`c)(2x-1)²+(x+3)²-(5x+1)(x+2)`
`=4x²-4x+1+x²+6x+9-(5x²+10x+x+2)`
`=4x²-4x+1+x²+6x+9-5x²-10x-x-2`
`=-9x+8`
`d)2(x-4)(x+4)-(2x+3)(x-7)`
`=2(x²-16)-(2x²-14x+3x-21)`
`=2x²-32-2x²+14x-3x+21`
`=11x-11`
`=11(x-1)`
