Câu a : \(\left(x^2+1\right)^2-4x^2\)
\(=\left(x^2+1\right)^2-\left(2x\right)^2\)
\(=\left(x^2+1-2x\right)\left(x^2+1+2x\right)\)
\(=\left(x-1\right)^2\left(x+1\right)^2\)
Câu b : \(16x^2-\left(x^2+4\right)^2\)
\(=\left(4x\right)^2-\left(x^2+4\right)^2\)
\(=\left(4x-x^2-4\right)\left(4x+x^2+4\right)\)
\(=-\left(x-2\right)^2\left(x+2\right)^2\)
\(a,\left(x^2+1\right)^2-4x^2\)
\(=\left(x^2+1-2x\right)\left(x^2+1+2x\right)\)
\(=\left(x-1\right)^2\left(x+1\right)^2\)
\(b,16x^2-\left(x^2+4\right)^2\)
\(=\left(4x-x^2-4\right)\left(4x+x^2+4\right)\)