= 28x^2n-1 + 4xⁿ⁺¹ - 20xⁿ - 28x^2n-1 + 20x² = 4xⁿ⁺¹

đúng 100%

\(4x^n\left(7x^{n-1}+x-5\right)-2x^{n-2}\left(14x^{n+1}-10x^2\right)\)

\(=28x^{2n-1}+4x^{n+1}-20x^n-28x^{2n-1}+20x^n\)

\(=4x^{n+1}\)

Giải: 

    4xⁿ (7x^n-1 + x - 5) - 2x^n-2 (14xⁿ⁺¹ - 10x²) 

      = 28x^2n-1 +4x^{n + 1}  – 20xⁿ  - 28x^2n-1 + 20xⁿ

       = 4xⁿ⁺¹

a: \(=2x+x^3-5x^4\)

b: \(=\dfrac{8x^2+4x-7x-3}{\left(2x-1\right)\left(2x+1\right)}=\dfrac{8x^2-3x-3}{\left(2x-1\right)\left(2x+1\right)}\)

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

\(=2x\left(x^2-2x+1\right)-3\left(x^2-2x+1\right)+2\left(2^3-3\cdot2^2\cdot x+3\cdot2\cdot x^2-x^3\right)\)

\(=2x^3-4x^2+2x-3x^2+6x-3+2\left(8-12x+6x^2-x^3\right)\)

\(=2x^3-4x^2+2x-3x^2+6x-3+16-24x+12x^2-2x^3\)

\(=\left(2x^3-2x^3\right)+\left(-4x^2-3x^2+12x^2\right)+\left(2x+6x-24x\right)+\left(-3+16\right)\)

\(=5x^2-16x+13\)

b)

 

Vậy \(\left(2x^3-7x^2+2x+3\right):\left(x^2-4x+3\right)=2x+1\)

Câu b thêm dấu " - " ở chỗ 2x³ - 7x² + 2x +3 và  2x³ - 8x² + 6x nhé :)))

\(=12x^{n+3}-8x^{n+2}\)