\(\left(x+1\right)\left(x+2\right)\left(x+5\right)-\left(x^3-8x^2\right)=\left(x^2+3x+2\right)\left(x+5\right)-x^3+8x^2=x^3+3x^2+2x+5x^2+15x+10-x^3+8x^2=16x^2+17x+10\)
Lời giải:
** Bạn chú ý viết đầy đủ yêu cầu của đề
$(x+1)(x+2)(x+5)-(x^3-8x^2)$
$=(x^2+3x+2)(x+5)-(x^3-8x^2)$
$=x^3+8x^2+17x+10-x^3+8x^2$
$=16x^2+17x+10$
x = -(3^(3/2)*căn bậc hai(13)*i+17)/32;x = (3^(3/2)*căn bậc hai(13)*i-17)/32;
Ta có: \(\left(x+1\right)\left(x+2\right)\left(x+5\right)-\left(x^3-8x^2\right)\)
\(=\left(x^2+3x+2\right)\left(x+5\right)-x^3+8x^2\)
\(=x^3+5x^2+3x^2+15x+2x+10-x^3+8x^2\)
\(=16x^2+17x+10\)