Ta có
\(B=-5x^3-\left(x^2-1\right)+5x+x^2-8x+3x^3\)
\(=-5x^3-x^2+1+5x+x^2-8x+3x^3\)
\(=-2x^3+1-3x\)
\(B=-5x^3-\left(x^2-1\right)+5x+x^2-8x+3x^3\)
\(B=-2x^3-3x+1\)
B=-5x3-(x2-1)+5x+x2-8x+3x3
B=(-5x3+3x3)+(x2-x2)+(5x-8x)+1
B=-2x3-3x+1
B = -5x3 - ( x2 - 1 ) + 5x + x2 - 8x + 3x3
= -5x3 - x2 + 1 + 5x + x2 - 8x + 3x3
= ( -5x3 + 3x3 ) + ( x2 - x2 ) + ( 5x - 8x ) + 1
= -2x3 - 3x + 1