a) `A=4x-(x+3)^2+(x+3)(x-3)`
`=4x-x^2-6x-9+x^2-9`
`=-2x-18`
Thay `x=2,4` vào `-2x-18` ta có:
`-2.2,4-18=-4,8-18=-22,8`
b) `B=(3x+4)^2-10x-9(x-4)(4+x)`
`=9x^2+24x+16-10x-36x-9x^2+144+36x`
`=14x+160`
Thay `x=-0,1` vào `14x+160` ta có:
`14.(-0,1)+160=-1,4+160=158,6`
c) `C=(x+5)^2-2(x-6)(x+6)+(x+2)(x-4)`
`=x^2+10x+25-2x^2-12x+12x+72+x^2-4x+2x-8`
`=8x+89`
Thay `x=-1/2` vào `8x+89` ta có:
`8. (-1/2)+89=-4+89=85`