Question

The formula S= n(a^1+ a^n)/ 2 gives partial sum of an arithmetic sequence. what is the formula solved for a^n?

options are;
1. a^n= 2S-a^1n/n
2. a^n= 2S+a^1n/n
3. a^n= 2S+a^1n+ n
4. a^n= 2S-a^1n+ n