Question

The fourth and sixth term of an arithmetic progession are -4 and -10 respectively. Find
A.the common difference
B.the first term
C.sum of the first twelve terms

Answer 1

d is easy, since A6-A4 = 2d, so

2d = -6

Now you can find a, since a+2d = -4

S12 = 12/2 (2a+11d)