a)
`A=(x+3)^2+(x-3)(x+3)-2(x+2)(x-4)`
`=x^2+6x+9+x^2-9-(2x+4)(x-4)`
`=x^2+6x+9+x^2-9-(2x^2-8x+4x-16)`
`=x^2+6x+9+x^2-9-2x^2+8x-4x+16`
`=(x^2+x^2-2x^2)+(6x+8x-4x)+(9-9+16)`
`= 10x+16`
Thay `x=-1/2` ta có:`10.-1/2+16=11`
b)
`B=(3x+4)^2-(x-4)(x+4)-10x`
`=9x^2+24x+16-(x^2-16)-10x`
`=9x^2+24x+16-x^2+16-10x`
`=(9x^2-x^2)+(24x-10x)+(16+16)`
`=8x^2+14x+32`
Thay `x=-1/10` ta có: `8.(-1/10)^2+14.-1/10+32=767/25`
c)
`C=(x+1)^2-(2x-1)^2+3(x-2)(x+2)`
`=x^2+2x+1-(4x^2-4x+1)+3(x^2-4)`
`=x^2+2x+1-4x^2+4x-1+3x^2-12`
`=(x^2+3x^2-4x^2)+(2x+4x)+(1-1-12)`
`= 6x-12`
Thay `x=1` ta có `6.1-12=-6`
