Question

calcule a soma dos termos da progressao aritmetica (10, 15, ...,1280)

Answer 1

resolução!

r = a2 - a1

r = 15 - 10

r = 5

an = a1 + ( n - 1 ) r

1280 = 10 + ( n - 1 ) 5

1280 = 10 + 5n - 5

1280 = 5 + 5n

1280 - 5 = 5n

1275 = 5n

n = 1275 / 5

n = 255

Sn = ( a1 + an ) n / 2

Sn = ( 10 + 1280 ) 255 / 2

Sn = 1290 * 255 / 2

Sn = 328950 / 2

Sn = 164475