\(A=\left(4x^3+16x^2+28x\right)-\left(x^2+4x+7\right)+a+11\\ A=\left(x^2+4x+7\right)\left(4x-1\right)+a+11\)
Để \(A⋮B\Leftrightarrow\left[\left(x^2+4x+7\right)\left(4x-1\right)+a+11\right]⋮\left(x^2+4x+7\right)\)
\(\Leftrightarrow a+11=0\\ \Leftrightarrow a=-11\)


