Đáp án:
Giải thích các bước giải:
`a) -4x^5 (x^3 -4x^2 +7x-3)`
`=-4x^5 .x^3 -4x^5 . (-4x^2) -4x^5 .7x -4x^5 .(-3)`
`=-4x^8 +16x^7 -28x^6 +12x^5`
`b) -4x(3x-4)+7x(x-5)`
`=-4x.3x -4x.(-4) +7x.x +7x.(-5)`
`= -12x^2 +16x +7x^2 -35x`
`=(-12x^2 +7x^2)+(16x-35x)`
`=-5x^2 -19x`
`c)(2x+3y)(3x+2y-1)`
`=2x.3x +2x.2y +2x.(-1) +3y.3x +3y.2y +3y.(-1)`
`=6x^2 +4xy -2x +9xy +6y^2 -3y`
`=6x^2 + (4xy +9xy) -2x+6y^2 -3y`
`=6x^2 +13xy -2x +6y^2 -3y`
`d)A= (5x-7)(2x+3)-(7x+2)(x-4)`
`= 5x.2x +5x.3 -7.2x -7.3 - [7x.x +7x.(-4) +2.x +2.(-4)]`
`=10x^2 +15x -14x -21 -7x^2 +28x -2x+8`
`=(10x^2 -7x^2)+(15x-14x+28x-2x)+(-21+8)`
`=3x^2 +27x -13`
Thay `x=1/2`
`=> 3.(1/2)^2 +27. 1/2 -13`
`=3. 1/4 + 27. 1/2 -13`
`=5/4`
