Question

a1=5 a2=7 a14-? S14-?

Answer 1

$d= a_{n+1} - a_{n}\\a_{n}=a_{1}+d(n-1)\\s_{n}= \frac{2a_{1}+d(n-1)}{2} *n \\\\d = 7-5=2\\a_{14} = 5+2(14-1)=5+2*13=5+26=31\\s_{14} = \frac{10+26}{2}*14=36*7=252$