Question

Khai triển biểu thức :

1, \(\left(2x-3y\right)^3\)

2, \(\left(2x+\dfrac{9}{2}\right)^3\)

3, \(\left(x+2y\right)^3+\left(x-2y\right)^3\)

4, \(\left(2x+1\right)^3-\left(x-1\right)^3-7\cdot\left(x+1\right)^3\)

Answer 1

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

b, \(\left(2x+\dfrac{9}{2}\right)^3=8x^3-54x^2+121,5x-91,125\)

c, \(\left(x+2y\right)^3+\left(x-2y\right)^3=x^3+6x^2y+12xy^2+8y^3+x^3-6x^2y+12xy^2-8y^3\)

\(=2x^3+24xy^3\)

d, \(\left(2x+1\right)^3-\left(x-1\right)^3-7\left(x+1\right)^3\)

\(=8x^3+12x^2+6x+1-\left(x^3-3x^2+3x-1\right)-7\left(x^3+3x^2+3x+1\right)\)

\(=8x^3+12x^2+6x+1-x^3+3x^2-3x+1-7x^3-21x^2-21x-7\)

\(=-6x^2-18x-5\)

Chúc bạn học tốt!!!