Bài 6:
a) Ta có: \(f\left(x\right)=-3x^2+x-1+x^4-x^3-x^2+3x^4\)
\(=4x^4-x^3-4x^2+x-1\)
Ta có: \(g\left(x\right)=x^4+x^2-x^3+x-5+5x^3-x^2\)
\(=x^4+4x^3+x-5\)
b) Ta có: f(x)-g(x)
\(=4x^4-x^3-4x^2+x-1-x^4-4x^3-x+5\)
\(=3x^4-5x^3-4x^2+4\)
Ta có: f(x)+g(x)
\(=4x^4-x^3-4x^2+x-1+x^4+4x^3+x-5\)
\(=5x^4+3x^3-4x^2+2x-6\)
c) \(g\left(-1\right)=\left(-1\right)^4+4\cdot\left(-1\right)^3+\left(-1\right)-5\)
\(=1-4\cdot1-1-5\)
\(=1-4-1-5\)
\(=-9\)
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