Question

giúp mk bài 3 nka :333

Answer 1

\(3,\\ A=1-8x^3+8x^3-8=-7\\ B=\left(3x-y\right)\left(9x^2+3xy+y^2\right)+x^3+y^3-27x^3\\ B=27x^3-y^3+x^3+y^3-27x^3=x^3\)

Answer 2

Bài 4: 

a: Ta có: \(x\left(x-5\right)\left(x+5\right)-\left(x+2\right)\left(x^2-2x+4\right)=17\)

\(\Leftrightarrow x^3-25x-x^3-8=17\)

\(\Leftrightarrow-25x=25\)

hay x=-1

b: Ta có: \(8\left(x-\dfrac{1}{2}\right)\left(x^2+\dfrac{1}{2}x+\dfrac{1}{4}\right)-4x\left(2x^2-x+1\right)+2=0\)

\(\Leftrightarrow8x^3-1-8x^3+4x^2-4x+2=0\)

\(\Leftrightarrow2x-1=0\)

hay \(x=\dfrac{1}{2}\)