Question

Find the sum of following series, x+y, x-y, x-3y,........22 terms

Answer 1

First term, a=(x+y)
Common difference, d=(-2y)
Sum up to 'n' terms, $S_{n}=\frac{n}{2}(2a+(n-1)d)$
Here n=22, then $S_{22}=\frac{22}{2}(2(x+y)+(22-1)(-2y))=22x-440y$.

Answer 2

Given term = x+y , x-y , x-3y
a=(x+y)
d= a₂-a₁
  = (x-y - x - y)
  = -2y

Sn = n/2[2a+(n-1)d]

S₂₂=22/2[(2*x+y)+(22-1)-2y)

     11(2x+2y-42y)     
     11(2x-40y)                                   
     22x-440y