Question

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

Answer 1

first term =(x+y)
common difference =x-y-x-y=-2y
now ,
Sn=n/2{2a+(n-1)d}

S22=22/2{2(x+y)+(22-1)(-2y)}
=11{2x+2y-42y)
=22x-440y