Question

S=n(a1+an)/2 gives the partial sum of an arithmetic sequence. What is the formula solved for an?

Answer 1

Just took the quiz.

The answer is an=2S-a1n/n

Answer 2

The given formula is
$S= \frac{n}{2} (a_{1}+a_{n})$

Multiply each side by 2.
$2S=n(a_{1}+a_{n})$

Divide each side by n.
$\frac{2S}{n} =a_{1} + a_{n}$

Subtract a₁ from each side.
$\frac{2S}{n} - a_{1} = a_{n}$

Answer: $a_{n} = \frac{2S}{n} - a_{1}$