1) \(\left(x+1\right)\left(x+2\right)-3x\left(x-4\right)=x^2+3x+2-3x^2+12x=-2x^2+15x+2\)

2) \(\left(3x-4\right)\left(x-2\right)=3x\left(x-9\right)\)

\(\Leftrightarrow3x^2-10x+8=3x^2-27x\)

\(\Leftrightarrow17x=-8\Leftrightarrow x=-\dfrac{8}{17}\)

3) \(-3\left(x-4\right)\left(x-2\right)-x^2\left(-3x+18\right)+24x-25\)

\(=-3x^3+6x^2+12x^2-24x+3x^3-18x^2+24x-25=-25\)

\(\left(3x-4\right)^2-2\left(3x-4\right)\left(x-4\right)+\left(x-4\right)^2\)

\(=\left(3x-4-x+4\right)^2\)

\(=4x^2\)

\(\left(3x-4\right)^2+\left(4-x\right)^2-2\left(3x-4\right)\left(x-4\right)=\left(3x-4\right)^2-2\left(3x-4\right)\left(x-4\right)+\left(x-4\right)^2=\left(3x-4-x+4\right)^2=\left(2x\right)^2=4x^2\)

a) (x²-1)(x²+4)(x²-4)=(x²-1)(x⁴-16)

b) 9x²+6x+1+4-9x²= 6x+5

`@` `\text {Ans}`

`\downarrow`

`a)`

`(3x^2 + 2x)*(x^2 - 3) + (4 - x^3) * (3x+2)`

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

`= 3x^4 - 9x^2 + 2x^3 - 6x + 12x + 8 - 3x^4 - 2x^3`

`= (3x^4 - 3x^4) + (2x^3 - 2x^3) - 9x^2 + (-6x+12x) + 8`

`= -9x^2 + 6x + 8`

\(\left(x+2\right)^2-\left(x+4\right)^2+x^2-3x+1\)

\(=x^2+4x+4-x^2-8x-16+x^2-3x+1\)

\(=x^2-7x-11\)

\(\left(x+2\right)^2-\left(x+4\right)^2+x^2-3x+1\)

\(=x^2+4x+4-x^2-8x-16+x^2-3x+1=x^2-7x-11\)

a: Ta có: \(x^2-4x\left(3x-4\right)+7x-5\)

\(=x^2-12x^2+16x+7x-5\)

\(=-11x^2+23x-5\)

b: Ta có: \(7x\left(x^2-5\right)-3x^2y\left(xy-6y^2\right)\)

\(=7x^3-35x-3x^3y^2+18x^2y^3\)

c: Ta có: \(\left(5x+4\right)\left(2x-7\right)\)

\(=10x^2-35x+8x-28\)

\(=10x^2-27x-28\)

bài này dễ vậy mà không làm được.Lười

bn ngon thì làm đi

a: \(A=x^2+2+3x^2+2-2x^2-2=2x^2+2\)

b: \(B=2x-3-\left(3x-2\right)-\left(2x-4\right)\)

\(=2x-3-3x+2-2x+4=-3x+3\)

c: \(C=6-3x+3x+10=16\)

d: \(D=\left|3x-8\right|+\left|x+2\right|\)

\(=3x-8+x+2=4x-6\)