Question

calcule a soma :
a) dos seis primeiros termos da pg (2,8...)
b)dos dez primeiros termos da pg (a^2,a^5,...)

Answer 1

a) $\boxed{S_n=\frac{a_1(q^n-1)}{q-1}}\\\\ S_6=\frac{2(4^6-1)}{4-1}\\\\ S_6=\frac{2(4096-1)}{3}\\\\ S_1_0=2*1365\\\\ \boxed{S_1_0=2730}$

b) $S_1_0 = \frac{a^2(a^3^(^1^0^)-1}{a^3-1}\\\\ S_1_0=\frac{a^2(a^3^0-1)}{a^3-1}\\\\ S_1_0=a^2(a^1^0)\\\\ \boxed{S_1_0=a^1^2}$