Bài 3:
\(P\left(x\right)+Q\left(x\right)=\left(4x^4-2x^3-7x^2+2x+\dfrac{1}{3}\right)+\left(x^4+3x^3-6x^2-x-\dfrac{1}{4}\right)\\ =4x^4-2x^3-7x^2+2x+\dfrac{1}{3}+x^4+3x^3-6x^2-x-\dfrac{1}{4}\\ =5x^4+x^3-13x^2-x+\dfrac{1}{12}\\ P\left(x\right)-Q\left(x\right)=\left(4x^4-2x^3-7x^2+2x+\dfrac{1}{3}\right)-\left(x^4+3x^3-6x^2-x-\dfrac{1}{4}\right)\\ =4x^4-2x^3-7x^2+2x+\dfrac{1}{3}-x^4-3x^3+6x^2+x+\dfrac{1}{4}\\ =3x^4-5x^3-x^2+3x+\dfrac{7}{12}\)
Đúng 4
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