1) a5=a2.q^3
a5= 10.(-5)^3
a5= 10.(-125) => -1250
2)a1, a2, a3, a4 portanto: (12, 12q, 12q^2, 96):
[tex]\frac{a_{2}}{a_{1}}=\frac{a_{4}}{a_{3}}=>\frac{12q}{12}=\frac{96}{12q^2}\\\\\frac{12q}{12}=\frac{96}{12q^2}=>q^3=8\\q=2[/tex]
3) a3, a4, a5, a6 então: (..., 40, 40q, 40q^2, 320,..., a8?):
[tex]\frac{a_{4}}{a_{3}}=\frac{a_{6}}{a_{5}}=>\frac{40q}{40}=\frac{320}{40q^2}\\\\q^3=8\\q=2[/tex]
a8=a3.q^5
a8=40.2^5
a8 = 960
4)[tex]a_{1}=5\ q=-4\ \ P.G.:\{5, -20, 80, -320, 1280\}.[/tex]
5)[tex]S_8=\frac{-6(1-(-2)^8)}{1-(-2)}=>\frac{-6(1-256)}{3}=510[/tex]
6)[tex] a_{2}=\sqrt{a_1.a_3}=>a_2=\sqrt{16*400}=>a_2=80\\\\q=\frac{a_2}{a_1}=>q=\frac{80}{16}=5\\\\a_5=a_1.q^4\\a_5=16.(5)^4=>a_5=10000\\a_4=\frac{a_5}{q}=>a_4=2000[/tex]
