Question

Calculate the sum of the first n terms of the arithmetic progression (an)

a) a, = -4; d = 2; n = 16
please help me

Answer 1

n²-5n

Explanation:

The sum of the nth term is expressed as;

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

Given

a, = -4; d = 2; n = 16

Sn = n/2[2(-4)+(n-1)2]

Sn =n/2[-8+2n-2]

Sn = n/2[2n-10]

Hence the sum of the nth term is 2n²-10n/2

2n(n-5)/2

= n(n-5)

= n²-5n

The sum of the nth term is n²-5n