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Calculati a8 stiind ca a2=5 si r=3
Calculati S10 stiind ca a1=7 si a7=37


Răspuns :

a₈=a₂+6r
a₈=5+18 =>a₈=23

a₁=7
a₇=37
a₇=a₁+6r
37=7+6r
6r=30 =>r=5
a₁₀=a₇+3r =52
S₁₀= (a₁+a₁₀) * 10 /2
S₁₀=(7+52) * 5
S₁₀=59 * 5
S₁₀=295