In the arithmetic sequence {an}, A5 = 10. A12 = 31, find the general term formula an, the first 10 terms and S10

In the arithmetic sequence {an}, A5 = 10. A12 = 31, find the general term formula an, the first 10 terms and S10

a5=a1+4d=10
a12=a1+11d=31
The solution is: A1 = - 2, d = 3
So an = a1 + (n-1) d = 3n-5
S10=(a1+a10)*10/2=(-2+25)*5=115

In the arithmetic sequence {an}, it is known that a 5 = 10, a 12 = 31

Let the tolerance of the arithmetic sequence {an} be D, from A5 = 10, A12 = 31, d = A12 − a57 = 3, from A5 = a1 + 4D = 10, A1 = - 2, then an = - 2 + (n-1) × 3 = 3n-5

Arithmetic sequence - 1,4,9 The general formula of is

an=a1+(n-1)d
=>an=5n-6