Tại x = 16 => x +1 = 17

Thay vào A ta được:

A = x⁴ - (x+1)x³ + (x+1)x² - (x+1)x + 20

A= x⁴ -(x⁴ + x³)  + (x³ + x²)  -(x² + x) +20

A= x⁴ - x⁴ - x³ + x³ + x² - x² -x + 20

A= - x+20

Mà  x = 16

=> A= -16 + 20 = 4

Vậy A= 4 khi x =16

bn viết từng câu đi mik giải cho

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

    \(=\left[\left(x+2\right)-\left(x-2\right)\right]\left[\left(x+2\right)^2+\left(x+2\right)\left(x-2\right)+\left(x-2\right)^2\right]\)

\(\left(-3x-2\right)^2+\left(3x+5\right)\left(5-3x\right)=-7\)

\(\Leftrightarrow9x^2+12x+4+15x-9x^2+25-15x=-7\)

\(\Leftrightarrow12x+36=0\Leftrightarrow x=-3\)

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

\(\Leftrightarrow x^3+2x^2+2x+2x^2+4x+4-x\left(x^2-16x+64\right)=16x^2-9\)

\(\Leftrightarrow x^3+4x^2+6x+4-x^3+16x^2-64=16x^2-9\)

\(\Leftrightarrow4x^2+6x-51=0\)

\(\cdot\Delta=6^2-4.4.\left(-51\right)=852\)

Vậy pt có 2 nghiệm phân biệt

\(x_1=\frac{-6+\sqrt{852}}{8}\);\(x_2=\frac{-6-\sqrt{852}}{8}\)

\(\left(x^2-4x\right)^2+2\left(x-2\right)^2=43\)

\(\Leftrightarrow x^4-8x^3+16x^2+2x^2-8x+8-43=0\)

\(\Leftrightarrow x^4-8x^3+18x^2-8x-35=0\)

\(\Leftrightarrow x^4+x^3-9x^3-9x^2+27x^2+27x-35x-35=0\)

\(\Leftrightarrow x^3\left(x+1\right)-9x^2\left(x+1\right)+27x\left(x+1\right)-35\left(x+1\right)=0\)

\(\Leftrightarrow\left(x+1\right)\left(x^3-9x^2+27x-35\right)=0\)

\(\Leftrightarrow\left(x+1\right)\left(x^3-5x^2-4x^2+20x+7x-35\right)=0\)

\(\Leftrightarrow\left(x+1\right)\left[x^2\left(x-5\right)-4x\left(x-5\right)+7\left(x-5\right)\right]=0\)

\(\Leftrightarrow\left(x+1\right)\left(x-5\right)\left(x^2-4x+7\right)=0\)

Vì \(x^2-4x+7< 0\)

\(\Leftrightarrow\orbr{\begin{cases}x+1=0\\x-5=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=-1\\x=5\end{cases}}}\)

Vậy....

bạn có thể giúp mình 2 câu còn lại ko ạ

tự làm đi dễ vầy

a du