Question

1. Sn = 5n2 + 3n
2. Sn = 3n2 - 4n
3. S14 = 1050,a = 10
4. Sn = 4n - n2​

Answer 1

Step-by-step explanation:

1. find an = Sn - Sn-1 = 10n-2

use it to get d = 10

2. Sn = 3n2 - 4n

an = Sn - Sn-1

=(3n2-4n) - {3(n-1)2-4(n-1)}

=(3n2-4n) - {3n2+3-6n-4n+4}

= -{7-6n}

an = 6n-7