Question

i)                   ( 3+ x)(x^2 -9) – (x -3)(x^2 + 3x +9)

ii)                ( x -2)( x^2 + 2x + 4) – (25 +x^3)

rút gọn biểu thức 

Answer 1

\(i,=\left(x-3\right)\left(x+3\right)^2-\left(x-3\right)\left(x^2+3x+9\right)\\ =\left(x-3\right)\left(x^2+6x+9-x^2-3x-9\right)\\ =3x\left(x-3\right)=3x^2-9x\\ ii,=x^3-8-25-x^3=-33\)

Answer 2

ii: Ta có: \(\left(x-2\right)\left(x^2+2x+4\right)-\left(x^3+25\right)\)

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

=-33