Question

Find the sum of the first 12 terms of the progression 5,3,1,-1,-3.......

Answer 1

Hey

a = 5

d = 3 - 5 = -2

n = 12

sn = n/2{2a+(n-1)d}

s12 = 12/2 { 2(5)+(12-1)(-2)}

= 6 {10-22}

= 6 x (-12)

= -72