To solve the problem of calculating the sum of the first (n) terms of the sequence (1,2,3,\dots,n), follow these steps:
Problem Analysis
The sequence (1,2,3,\dots,n) is an arithmetic sequence where:
- First term (a_1 = 1)
- Common difference (d = 1)
- (n)-th term (a_n = n)
Sum Formula for Arithmetic Sequences
The sum (S) of the first (n) terms of an arithmetic sequence is:
[ S = \frac{n}{2} \times (a_1 + a_n) ]
Substitute Values
Since (a_1 =1) and (a_n =n):
[ S = \frac{n}{2} \times (1 + n) = \frac{n(n+1)}{2} ]
Example
For (n=5):
[ S = \frac{5(5+1)}{2} = \frac{5\times6}{2}=15 ]
Which matches (1+2+3+4+5=15).
Final Answer: The sum of the first (n) terms is (\boxed{\frac{n(n+1)}{2}}).
If you need the sum for a specific (n), replace (n) with the number (e.g., (n=10) gives (\boxed{55})).
Let me know if you have a specific (n) value!


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