用数学归纳法证明1+2+3+…+n=n(n+1)/2

Question

用数学归纳法证明1+2+3+…+n =n(n+1)/2

Answer 1

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