\(a,\)Thu gọn :
\(h\left(x\right)=4x^4-5x^2+2x+7\)
\(g\left(x\right)=4x^4-7x^2-3x+4\)
\(b,k\left(x\right)+h\left(x\right)=g\left(x\right)\)
\(\Rightarrow k\left(x\right)=g\left(x\right)-h\left(x\right)\)
\(\Rightarrow k\left(x\right)=4x^4-7x^2-3x+4-4x^4+5x^2-2x-7\)
\(\Rightarrow k\left(x\right)=-2x^2-5x-3\)
\(c,\)Đặt \(k\left(x\right)=0\)
\(\Rightarrow-2x^2-5x-3=0\)
\(\Rightarrow-2x^2-2x-3x-3=0\)
\(\Rightarrow-2x\left(x+1\right)-3\left(x+1\right)=0\)
\(\Rightarrow\left(x+1\right)\left(-2x-3\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x=-1\\x=-\dfrac{3}{2}\end{matrix}\right.\)
Vậy nghiệm của đa thức \(k\left(x\right)\) là \(-1;-\dfrac{3}{2}\)