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b1=-2
q=3
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b3,S4
Calculați progresia geometrica


Răspuns :

b₃=b₁×q²

b₃= -2×3²

b₃= -2×6

b₃= -12

S₄=b₁×(q⁴-1)/(q-1)

S₄= -2×(3⁴-1)/(3-1)

S₄= -2×(81-1)/2

S₄= -2× 80/2

S₄= -2×40

S₄= -80