Question

Q7

Answer 1

Answer:  d = 4, n = 14

Step-by-step explanation:

$S_n=\dfrac{a_1+a_n}{2}\cdot n$

$\text{Given:}\quad S_n=196, a_1=-12, a_n=40\\\\\\196=\dfrac{-12+40}{2}\cdot n\\\\392=28n\\\\14=n$

$a_{n}=a_1+d(n-1)\\a_{14}=a_1+d(14-1)\\40=-12+d(14-1)\\52 = 13d\\4=d$