高考真题理科系列
解BN =(-1)(n-1)* 4n/an * a(n+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)]
=(-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)]
=(-1)^(n-1)*[1/(2n-1)+1/(2n+1)]