=(-1)^(n-1)*4n/(2n-1)*( 2n 1)
=(-1)^(n-1)*[((2n 1) (2n-1))/(2n-1)*(2n 1)]
=(-1)^(n-1)*[(2n 1)/(2n-1)*(2n 1) (2n-1)/(2n-1)*(2n 1)] p>
=(-1)^(n-1)*[1/(2n-1) 1/(2n 1)]
=(-1)^(n-1)*4n/(2n-1)*( 2n 1)
=(-1)^(n-1)*[((2n 1) (2n-1))/(2n-1)*(2n 1)]
=(-1)^(n-1)*[(2n 1)/(2n-1)*(2n 1) (2n-1)/(2n-1)*(2n 1)] p>
=(-1)^(n-1)*[1/(2n-1) 1/(2n 1)]