ace ơi cứu t
a, \(A\left(x\right)=x^3\left(x+2\right)-5x+9+2x^3\left(x-1\right)\)
\(=x^4+2x^3-5x+9+2x^4-2x^3=3x^4-5x+9\)
\(B\left(x\right)=2\left(x^2-3x+1\right)-\left(3x^4+2x^3-3x+4\right)\)
\(=2x^2-6x+2-3x^4-2x^3+3x-4=-3x^4-2x^3+2x^2-3x-2\)
b, \(A\left(x\right)+B\left(x\right)=3x^4-5x+9-3x^4-2x^3+2x^2-3x-2=-2x^3+2x^2-8x+7\)
\(A\left(x\right)-B\left(x\right)=3x^4-5x+9+3x^4+2x^3-2x^2+3x+2=6x^4+2x^3-2x^2-2x+11\)
c, \(A\left(x\right)+B\left(x\right)=-2x^3+2x^2-8x+7=0\Leftrightarrow x=0,895\)
d, \(H\left(x\right)=A\left(x\right)+5x=3x^4+9=0\)
Mà \(3x^4\ge0\Rightarrow3x^4+9>0\forall x\)
Vậy pt vô nghiệm
a)
\(A\left(x\right)=x^3\left(x+2\right)-5x+9+2x^3\left(x-1\right)\\ =x^4+2x^3-5x+9+2x^4-2x^3\\ =9-5x+3x^4\)
\(B\left(x\right)=2\left(x^2-3x+1\right)-\left(3x^4+2x^3-3x+4\right)\\ =2x^2-6x+2-3x^4-2x^3+3x-4\\ =-2-3x+2x^2-2x^3-3x^4\)
b)
\(A\left(x\right)+B\left(x\right)=\left(9-5x+3x^4\right)+\left(-2-3x+2x^2-2x^3-3x^4\right)\\ =9-5x+3x^4-2-3x+2x^2-2x^3-3x^4\\ =-2x^3+2x^2-8x+7\)
\(A\left(x\right)-B\left(x\right)=\left(9-5x+3x^4\right)-\left(-2-3x+2x^2-2x^3-3x^4\right)\\ =9-5x+3x^4+2+3x-2x^2+2x^3+3x^4\\ =6x^4+2x^3-2x^2-2x+11\)
