n thuộc N
B=x^2 +2x +1 =(x+1)^2
\(A=x^{4n+2}+2.x^{2n+1}+1=\left(x^{2n+1}\right)^2+2.\left(x^{2n+1}\right)+1=\left(x^{2n+1}+1\right)^2\)
\(\dfrac{A}{B}=\left(\dfrac{x^{2n+1}+1}{x+1}\right)^2\)
với n =0 đúng
n >0 =>2n+1 >=3
=> x^(2n+1) =(x+1).g(x) => dpcm