Question

Dany jest ciąg geometr. 2,4,8.... podaj a20 i S10

Answer 1

q = a2 / a1 = 4/2 = 2

q = 2

a1 = 2

an = a1 * q ^n-1

a20 = 2 * 2^19 = w^1 + 2^19 = 2^20

Sn = a1 * (1 - q^n)/(1-q)

S10 = 2 * (1-2^10)/(1-2) = 2* [-(1-2^10)] =  2* (-1 + 2^10) = -2 + 2^11