Bài toán `7.`

`a)`

`A=(3x+2)^2-2(x-1)^2-7x^2`

`A=(9x^2+12x+4)-2(x^2-2x+1)-7x^2`

`A=9x^2+12x+4-2x^2+4x-2-7x^2`

`A=(9x^2-2x^2-7x^2)+(12x+4x)+(4-2)`

`A=16x+2`

Vậy `A=16x+2`

`b)`

`B=2(x-y)(x+y)+(x+y)^2+(x-y)^2`

`B=[(x+y)+(x-y)]^2`

`B=(x+y+x-y)^2`

`B=(2x)^2`

`B=4x^2`

Vậy `B=4x^2`

`c)`

`C=(4x^2+y^2)(2x+y)(2x-y)`

`C=(4x^2+y^2)[(2x)^2-y^2]`

`C=(4x^2+y^2)(4x^2-y^2)`

`C=(4x^2)^2-(y^2)^2`

`C=16x^4-y^4`

Vậy `C=16x^4-y^4`

`d)`

`D=(a+2)^2-(a+2)(a-2)`

`D=(a+2)[(a+2)-(a-2)]`

`D=(a+2)(a+2-a+2)`

`D=(a+2).4`

`D=4a+8`

Vậy `D=4a+8`

`e)`

`E=(3x+4)^2-(x-4)(x+4)-10x`

`E=(9x^2+24x+16)-(x^2-16)-10x`

`E=9x^2+24x+16-x^2+16-10x`

`E=(9x^2-x^2)+(24x-10x)+(16+16)`

`E=8x^2+14x+32`

Vậy `E=8x^2+14x+32`