6A
\(\left(-3x^2y^3z+9x^3y^2z^2-12x^4yz^2\right):\left(-3xyz\right)=\dfrac{-3x^2y^3z}{-3xyz}+\dfrac{9x^3y^2z^2}{-3xyz}+\dfrac{-12x^4yz^2}{-3xyz}=xy^2-3x^2yz+4x^3z\)
7A\(f\left(x\right)-g\left(x\right)=x^4-3x^3+x^2-x+10-\left(2x^4-2x^2+x-5\right)=x^4-3x^3+x^2-x+10-2x^4+2x^2-x+5=-x^4-3x^3+3x^2-2x+15\)
8B
\(A=\left(4x-6\right)\left(x+7\right)-4x\left(x+5\right)-2x=4x^2+22x-42-4x^2-20x-2x=-42\)
\(-42< -1\Rightarrow A< -1\)
9C
Thay x=1,y=1 ta được: \(1^{n-1}\left(1+1\right)-1\left(1^{n-1}+1^{n-1}\right)=1.2-\left(1+1\right)=0\)
Phần mấu chốt là \(1^{n-1}=1\) với mọi n
10D
\(15x^3yz^5.\left(-3y^3z^2\right)=-45x^3y^4z^7\)
Đúng 1
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