Question

Calcular os 5 primeiros termos de uma P.G, dados a1= -5 e q= -2

Answer 1

Basta utilizar a equação do termo geral da PG, acompanhe:

$\boxed{a_n~=~a_m.q^{n-m}}\\\\\\\\a_2~~=~~a^1.q^{2-1}~~=~-5~.~(-2)^1~~=~-5~.~(-2)~~\rightarrow~\boxed{a_2~=~10}\\\\\\a_3~~=~~a^2.q^{3-2}~~=~~10~.~(-2)^1~~=~~10~.~(-2)~~\rightarrow~\boxed{a_3~=\,-20}\\\\\\a_4~~=~~a^3.q^{4-3}~~=~-20~.~(-2)^1~~=~-20~.~(-2)~~\rightarrow~\boxed{a_4~=~40}\\\\\\a_5~~=~~a^5.q^{5-4}~~=~~40~.~(-2)^1~~=~~40~.~(-2)~~\rightarrow~\boxed{a_5~=\,-80}$

A PG fica:  -5 , 10 , -20 , 40 , -80