a: =18x^3y^2-12x^3y^3+6x^2y^2

b: (-3x+2)(5x^2-1/3x+4)

=-12x^3+x^2-12x+10x^2-2/3x+8

=-12x^3+11x^2-38/3x+8

c: =x^2-x-2+3x-x^2

=2x-2

d: =4x^2+12x+9-4x^2+25-(x-1)(x^2+12)

=12x+34-x^3-12x+x^2+12

=-x^3+x^2+46

`Answer:`

`a)`

`A=5(x+1)^2-3(x-3)^2-4(x^2-4)`

`=>A=5(x^2+2x+1)-3(x^2-6x+9)-4x^2+16`

`=>A=5x^2+10x+5-3x^2+18x-27-4x^2+16`

`=>A=(5x^2-3x^2-4x^2)+(10x+18x)+(5-27+16)`

`=>A=-2x^2+28x-6`

`b)`

`B=5(x+1)^2-3(x-3)^2-4(x+2)(x-2)`

`=2x(3x+5)-3(3x+5)-2x(x^2-4x+4)-[(2x)^2-3^2]`

`=6x^2+10x-9x-15-2x^3+8x^2-8x-4x^2+9`

`=(6x^2-4x^2+8x^2)-2x^3+(10x-9x-8x)+(-15+9)`

Thay `x=-7` vào ta được:

`B=10(-7)^2-2(-7)^3-7(-7)-6`

`=>B=10.49-2(-343)+49-6`

`=>B=490+686+49-6`

`=>B=1219`

\(a,B=4x^2+20x+25-9+x^2+14=5x^2+20x+30\\ b,B=5\left(x^2+4x+4\right)+10\\ B=5\left(x+2\right)^2+10\ge10>0,\forall x\)

Do đó B luôn dương với mọi x

A = (x - 1)³ - x(x - 2)² + 1

A = (x - 1)(x² - 2x + 1) - x(x - 2)² + 1

A = x(x² - 2x + 1) - (x² - 2x + 1) - x(x - 2)² + 1

A = x³ - 2x² + x - (x² - 2x + 1) - x(x² - 2x.2 + 2²) + 1

A = x³ - 2x² + x - (x² - 2x + 1) - (x³ - 4x² + 4x) + 1

A = x³ - 2x² + x - x² + 2x - 1 - x³ + 4x² - 4x + 1

A = (x³ - x³) + (-2x² - x² + 4x²) + (x + 2x - 4x) + (-1 + 1)

A = x² - x

B = (-x - 2)³ + (2x - 4)(x² + 2x + 4) - x²(x - 6)

B = (-x - 2)[(-x²) - 2.(-x).2 + 2²] + (2x - 4)(x² + 2x + 4) - x²(x - 6)

B = -x[(-x)² - 2.(-x).2 + 2²] - 2[(-x)² - 2.(-x).2 + 2²] + (2x - 4)(x² + 2x + 4) - x²(x - 6)

B = -(x³ + 4x² + 4x) - (2x² + 4x + 8) + 2x(x² + 2x + 4) - 4(x² + 2x + 4) - x²(x - 6)

B = -(x³ + 4x² - 4x) - (2x² + 4x + 8) + 2x³ + 4x² + 8x - (x² + 8x + 16) - (x³ - 6x²)

B = -x³ - 4x² + 4x - 2x² - 4x - 8 + 2x³ + 4x² + 8x - x² - 8x - 16 - x³ + 6x²

B = (-x³ + 2x³ - x³) + (-4x² - 2x² + 4x² - x² + 6x²) + (-4x - 8x + 8x - 8x) + (-8 - 16)

B = -12x - 24

a: Ta có: \(\left(x+5\right)^2-4x\left(2x+3\right)^2-\left(2x-1\right)\left(x+3\right)\left(x-3\right)\)

\(=x^2+10x+25-4x\left(4x^2+12x+9\right)-\left(2x-1\right)\left(x^2-9\right)\)

\(=x^2+10x+25-16x^3-48x^2-36x-2x^3+18x+x^2-9\)

\(=-18x^3-46x^2-8x+16\)

A = 2x-3 -x+5 = x+2

A = 2x -3 +x-5 = 3x -8

câu B cũng có 2 truong hop tuong tu

\(\text{ 2x.(x-2)+(x+3).(1-2x)}\\ =\left(2x^2-4x\right)+\left(x-2x^2+3-6x\right)\\ =2x\left(x-2\right)+\left(-5-2x^2+3\right)\)