Question

(2, 4, 6, 8, 10, 12) dada a sequencia, qual a soma dos 20 primeiros termos?

Answer 1

2+4+6+8+10+12+14+16+18+20+22+24+26+28+30+32+34+36+38+40=420

Answer 2

an = a1 + (n-1).r

a20 = 2 + (20-1).2

a20 = 2+ (19).2

a20 = 40

Sn = (a1 + an). n / 2

S20 = (2 + a20). 20 / 2

S20 = (2 + 40). 20 / 2

S20 = (42). 20 / 2

S20 = 420