Compute the sum 1+2+3+⋯+n1 + 2 + 3 + \cdots + n1+2+3+⋯+n using the formula, and determine the formula.
fracn(n+1)2\\frac{n(n+1)}{2}fracn(n+1)2
n2n^2n2
fracn2+n+22\\frac{n^2+n+2}{2}fracn2+n+22
n(n−1)n(n-1)n(n−1)