Question

Viết theo HĐT
a) (x - 1)³
b) (2x + 3y)³
c) x³– 64.
d) 27x³+ 8y³
.
Bài 3. Tìm x, biết:
a) (x – 2)³– x²(x – 6) = 5

b) (x – 1)(x²+ x + 1) – x(x + 2)(x – 2) = 4

c) (x + 2)³– (x + 2) = 0
Bài 4. Tìm x biết (x + 2021)³+ (3x - 2022)³=(4x– 1)³

Answer 1

a) \(\left(x-1\right)^3\)

\(=x^3-3x^2+3x-1\)

b) \(\left(2x-3y\right)^3\)

\(=\left(2x\right)^3-3\left(2x\right)^23y+3.2x\left(3y\right)^3+\left(3y\right)^3\)

\(=8x^3-36x^2y+54xy^2-27y^3\)

 

Answer 2

Bài 3: 

a: Ta có: \(\left(x-2\right)^3-x^2\left(x-6\right)=5\)

\(\Leftrightarrow x^3-6x^2+12x-8-x^3+6x^2=5\)

\(\Leftrightarrow12x=13\)

hay \(x=\dfrac{13}{12}\)

b: Ta có: \(\left(x-1\right)\left(x^2+x+1\right)-x\left(x+2\right)\left(x-2\right)=4\)

\(\Leftrightarrow x^3-1-x^3+4x=4\)

\(\Leftrightarrow4x=5\)

hay \(x=\dfrac{5}{4}\)