a1=4*1-1=3 a5=4*5-1=19
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S₅=[(a₁+a₅)/2]×5
gdzie:
a₁ = 4×1 - 1 = 3
a₅ = 4×5 - 1 = 19
Po podstawieniu:
S₅ = [(3+19)/2]×5 = 11×5 = 55
Odpowiedź d)55
pzdr'**
a1=4*1-1=3
a5=4*5-1=19