Use Summation Notation
-3 + 6 + 9 + . . . + 21
A) $\sum _ { i = 1 } ^ { 7 } 3 i$
B) $\sum _ { i = 0 } ^ { 7 } 3 i$
C) $\sum _ { i = 1 } ^ { 7 } i ^ { 2 }$
D) $\sum _ { i = 1 } ^ { 7 } 3 i ^ { 2 }$

Question

Use Summation Notation
-3 + 6 + 9 + . . . + 21 
A) $\sum _ { i = 1 } ^ { 7 } 3 i$
B) $\sum _ { i = 0 } ^ { 7 } 3 i$
C) $\sum _ { i = 1 } ^ { 7 } i ^ { 2 }$
D) $\sum _ { i = 1 } ^ { 7 } 3 i ^ { 2 }$

Quizplus · Accepted Answer

The sequence is an arithmetic sequence with a common difference of 3, starting from 3 and ending at 21. The formula for the nth term of an arithmetic sequence is $a_n = a_1 + (n - 1)d$, where $a_1$ is the first term and $d$ is the common difference. Here, $a_1 = 3$ and $d = 3$, so the nth term is $3n$, which matches option A, where $i$ represents the term number, starting from 1 up to 7 (since $3 \times 7 = 21$).

Use Summation Notation -3 + 6 + 9 ∑i=173i\sum _ { i = 1 } ^ { 7 } 3 i∑i=17​3i

Use Summation Notation
-3 + 6 + 9 $\sum _ { i = 1 } ^ { 7 } 3 i$