Question

Question 3 (ii)
In an AP:
(ii) Given a = 7, $a_{13}=35$, find d and $S_{13}$.

Answer 1

(ii) $Giventhat,a=7,a_{13}=35.a_n=a+(n-1)d,\Rightarrow 35=7+(13-1)d\Rightarrow 12d=28\Rightarrow d=\frac{28}{12}=2.33Now,S_n=\frac{n}{2}(a+a_n)S_{13}=\frac{13}{2}(7+35)=273$