Use Mathematical Induction to Solve for All Positive Integers N $1 + 2 + 3 + 4 + \ldots + n = ?$

Multiple Choice

Use mathematical induction to solve for all positive integers n.​ $1 + 2 + 3 + 4 + \ldots + n = ?$ ​

A) $\frac { n ( n + 1 ) } { 2 }$
B) $\frac { ( n + 1 ) } { 2 }$
C) $\frac { n } { 2 } ( 3 n + 1 )$
D) $\frac { n ( n + 1 ) ( 1 n + 1 ) } { 6 }$
E) $\frac { n ^ { 2 } ( n + 1 ) ^ { 2 } } { 3 }$