Question

用数学归纳法证明1+2+3+…+n =n(n+1)/2

急求……

Answer 1

1、当n=1时，1=1，成立
2、设当n=k时，1+2+3+4+···+k=k（k+1）/2
则 当n=k+1时，1+2+····+k+（k+1）=k（k+1）/2+k+1=（k+1）（k+2）/2，成立
综上所述，原命题成立

Answer 2

n=1
LS =1
RS=1
n=1 is true
Assume n=k is true
1+2+3+..+k = k(k+1)/2
for n=k+1
LS
=1+2+3+..+k+(k+1)
= k(k+1)/2+ (k+1)
=(k+1)(k+2)/2 =RS
By principle of MI , it is true for all n