Verify the formula for $n = 1,2,3$, and 4 . Is it correct?
$$5 + 10 + 15 \cdots + 5 n = \frac { 2 n ( n + 1 ) } { 2 }$$
A) no
B) yes

Question

Quizplus · Accepted Answer

The given formula is incorrect. The correct formula for the sum of the arithmetic series $5 + 10 + 15 + \cdots + 5n$ is $\frac{n(5 + 5n)}{2}$ or $\frac{5n(n + 1)}{2}$, not $\frac{2n(n + 1)}{2}$ as stated. The given formula simplifies to $n(n + 1)$, which does not correctly represent the sum of the series.

Verify the Formula For n=1,2,3n = 1,2,3n=1,2,3 , and 4 Is It Correct

Verify the Formula For $n = 1,2,3$ , and 4 Is It Correct