Write the Sum Using Summation Notation $$a + a r + a r ^ { 2 } + a r ^ { 3 } + \ldots + a r ^ { 19 }$$

Multiple Choice

Write the sum using summation notation.
- $$a + a r + a r ^ { 2 } + a r ^ { 3 } + \ldots + a r ^ { 19 }$$

A) $\sum _ { i = 1 } ^ { 19 } a r ^ { j - 1 }$
B) $\sum _ { i = 1 } ^ { 20 } a r ^ { i - 1 }$
C) $\sum _ { i = 1 } ^ { 19 } a r ^ { i }$
D) $\sum _ { i = 1 } ^ { 20 } a r ^ { i }$