Question

rút gọn biểu thức :

a,27(1-x)(x^2+x+1)+81x(x-1)

b,y[x^2+x(x-y)+(x-y)^2]+(x-y)^3

Answer 1

a) \(27\left(1-x\right)\left(x^2+x+1\right)+81x\left(x-1\right)\)

\(=27\left(1-x^3\right)+81\left(x^2-x\right)\)

\(=27-27x^3+81x^2-81x\)

b) \(y\left[x^2+x\left(x-y\right)+\left(x-y\right)^2\right]+\left(x-y\right)^3\)

\(=y\left[x^2+x^2-xy+x^2-2xy+y^2\right]+x^3-3x^2y+3xy^2-y^3\)

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

\(=3x^2y-3xy^2+y^3+x^3-3x^2y+3xy^2-y^3=x^3\)

Answer 2

a, \(27\left(1-x\right)\left(x^2+x+1\right)+81x\left(x-1\right)=27-27x^3+81x^2-81x\)

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

\(=3x^2y-3xy^2+y^3+x^3-3x^2y+3xy^2-y^3=x^3\)