Find the sum of a+b, a-b, a-3b, ...... to 22 terms.
Ans: a + b, a - b, a - 3b, up to 22 terms d= a - b - a - b = 2b
S22 =22/2 [2(a+b)+21(-2b)]
11[2a + 2b - 42b]
= 22a - 440b Ans.