Mathematic Problems

2xn-2x-n2xn+4x-n+4

2xn-x-n2xn+x-n+2

2xn-x-n2xn+x-n+2

=xn-1xnxn+1xn+2

=xn·xn-1xnxn·xn+1+2xnxn

=x2n-1xnx2n+2xn+1xn

=xnx2n-1xnx2n+2xn+1

=x2n-1x2n+2xn+1

=xn2-1x2n+2xn+1

=xn-1xn+1xn+12

=xn-1xn+1