用数学归纳法证明:1-3+5-7+...+(-1)^N-1(2N-1)=(-1)^N-1*N
1个回答

解假设n=k命题成立

即1-3+5-7+...(-1)^(k-1)(2k-1)=(-1)^(k-1)*k

那么当n=k+1时,

1-3+5-7+...(-1)^(k-1)(2k-1)+(-1)^(k)(2(k+1)-1)

=1-3+5-7+...(-1)^(k-1)(2k-1)+(-1)^(k)(2k+1)

=(-1)^(k-1)*k+(-1)^(k)(2k+1)

=(-1)^(k-1)*k+(-1)^(k-1)*(-1)^(1)(2k+1)

=(-1)^(k-1)*k+(-1)^(k-1)*(-2k-1)

=(-1)^(k-1)[k+(-2k-1)]

=(-1)^(k-1)[-k-1]

=(-1)^(k-1)(-1)^(1)[k+1]

=(-1)^(k)(k+1)