Question

3) Calcule a Soma da P.A. (2,5, ..., 23).*​

Answer 1

Resolucao!

r = a2 - a1

r = 5 - 2

r = 3

an = a1 + ( n - 1 ) r

23 = 2 + ( n - 1 ) 3

23 = 2 + 3n - 3

23 = - 1 + 3n

23 + 1 = 3n

24 = 3n

n = 24/3

n = 8

Sn = ( a1 + an ) n / 2

Sn = ( 2 + 23 ) 8 / 2

Sn = 25 * 4

Sn = 100