20.O terceiro termo dessa P.G vale
a( )3
b( )9
c( )18
d( )27
PG
u1 + u3 = 20
u2 + u4 = 60
u1 + u1*q² = 20
u1*q + u1*q³ = 60
u1*(1 + q²) = 20
u1*q*(1 + q²) = 60
q = 60/20 = 3
u1*(1 + 9) = 20
u1 = 20/10 = 2
u3 = u1*q² = 2*9 = 18 (C)
pronto
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Verified answer
PG
u1 + u3 = 20
u2 + u4 = 60
u1 + u1*q² = 20
u1*q + u1*q³ = 60
u1*(1 + q²) = 20
u1*q*(1 + q²) = 60
q = 60/20 = 3
u1*(1 + 9) = 20
u1 = 20/10 = 2
u3 = u1*q² = 2*9 = 18 (C)
pronto